What % would you allocate to car performance vs. reliability?

No such thing as 100% reliability.
You are correct.. but the toyota and honda 4 cyl engines are close. The straight 6 ford 240 ci and 300 ci can go forever.

The toyota 4.7 v8 with timing belts can go a million miles and often has. The 5 speed toyota auto trans can run 15 years as well.. so there are cases of near perfect design that you can buy.
Ummm, the Modular was, and is, one of the best engines ever made. Also, the V8 you are alluding to was the Windsor, not the Lima, the Lima engines are V6's. The Modular family has been on Ward's Best list an obscene number of times all the way back to 1996, most recently with the Coyote in 2019.

But you've inadvertently, with the above gaffes, touched-on some of the necessary nuance/details that are oft missed when somebody tries to broad-brush a topic such as this.

The Modular was developed as a "modernized" version of the 427 SOHC, originally under the "Hurricane" moniker. It was designed to improve on some of the weaknesses/shortfalls of the pushrod Windsor, such as the bottom-end, so it featured a deep skirted multi-bolt main configuration along with side bolts.

It was originally a 4" bore design (like the Windsor) but because there were some plans to fit it to a FWD configuration (the Continental) the design was revised and the bore size, and spacing, reduced so that this was possible. The original design was shelved.

The first variant of this engine was introduced as the 4.6L 2V in the Panther cars. The engine was unremarkable. Power was similar to the outgoing Windsor (302). The engine was reliable. It eventually made its way into the Mustang and F-series trucks.

A taller deck height (5.4L) and V10 (6.8L) version were also introduced to provide more HP/torque for truck and SUV applications.

The PI version was introduced in the late 90's, which featured revised pistons (dished), camshafts and cylinder heads that flowed better. However, a design decision was made in order to expedite assembly on both the 32-valve (DOHC) and 16-valve (SOHC) engines that involved more of a "lead" in the spark plug holes so that they would self-centre. This reduced the number of threads that actually engaged the plug (3-4 at the bottom of the hole) and resulted in a situation where, if those threads were damaged, say during a plug change, that one could eject. This was corrected around 2002-2003 when the process was modified to be feature fully-threaded plug holes again.

The 2V modular engines enjoyed a very long production run and had a reputation for dependable service. The million mile Ford van is but one example. The obsession with the panther cars, many which were former LEO, taxi or Limo service tells that story well. An extremely robust powertrain that's relatively simple to work on and will go obscene distances with minimal maintenance.

Along with the 2V modular, its DOHC siblings, mainly the 5.4L in the Navigator, 4.6L in the Continental, 4.6L in the Mustang Cobra and the supercharged variants also saw excellent service. The 4.6L DOHC mill was eventually replaced by the 5.0L Coyote, which was the next generation of this platform.

Somewhere around 2005 Ford introduced the 3V engines which were an SOHC design that had variable cam timing. These engines were designed to improve performance but experienced problems with the phaser system as well as spark plugs that would break-off in the heads, requiring considerable effort to remove. This variant does not have the reputation for reliability of its predecessors. This engine is no longer in production.

Hurricane was eventually renamed "BOSS" and introduced as the 6.2L in the Raptor, eventually making its way into other trucks.

Because not everybody wants a gas-sucking 6.0L engine, so different sizes, which make different amounts of power, are produced to satisfy that need. Same reason Ford produced 4.6L, 5.4L and 6.8L versions of the Modular.

The venerable SBC (5.7L and 5.0L/350 and 305) engines were replaced by better ones, just like with the Windsor, that addressed similar deficiencies. The LSx engines are better in every respect than the old SBC.

The C4 featured different performance variants of the SBC, the same engine you just lamented the loss of above. The L98, LT1 and LT4 are all 350ci SBC's. The SBC saw numerous "tweaks" over the years, such as different fuel injection systems, as those evolved, and different ignition systems, such as going from HEI to Optispark, where the distributor was moved from the back, squeezed under the cowling at the firewall, to the timing cover, where it was driven off the cam gear.

Chrysler's MDS system has been extremely reliable. While there have been some lifter failures, that's a supplier problem with the lifters themselves and has nothing to do with the variable displacement system and has impacted non-MDS engines as well. GM has had a similar problem with their AFM engines, also lifter failures, likely the same supplier. However, GM also had a problem with their AFM engines consuming oil, a problem FCA hasn't had.

Honda's VTEC is their variable valve timing (not displacement) system. Their variable displacement system was called VCM and because it didn't alternate cylinders and some other poor choices, had a tendency to create sludge/varnish. @Trav has a lot of experience dealing with this in the Honda V6's.

The main complaints about MDS are the "stumble" you might experience if you kick it out of MDS when it's trying to shift or accelerate at low RPM, the rumble, which in some platforms that don't have the active isolators, you can feel, and the exhaust note, which, if you have aftermarket exhaust, gets a bit funky when it's running as a 4-pot. I own two MDS equipped vehicle and other than the exhaust note, it is mostly imperceptible on the RAM because of the active isolation system which uses frame-mounted electronic dampening devices that cancel out the MDS "rumble". The SRT, I'm sitting much closer to the engine and it lacks that feature, so you can feel a bit of a rumble when it goes in and out of MDS, though you can't really hear it in the exhaust because that's factory.

I've owned 4x 6.4L MDS vehicles and 2x 5.7L MDS ones. We also have a small fleet of RAM 1500's at work. We've had absolutely zero issues with the system over roughly a combined fleet mileage of ~1.4 million miles (2.1 million Km) and only one case of lifter failure.
The 3 valve 5.4 ford engines have too small oil passages. And the plastic timing chain parts break off and make a mess. You lose a seal on the valve timing stuff on one side and have no oil pressure on the other side. What a pos.

The bmw v8s that have bearing issues are just a sad engineering failure. The valve guide failures costs more to fix than the cars are worth. The bmw x5 can often be complete failures and a disgrace to modern car quality.
I have been family suv shopping.. tahoes have engine and trans failures. Cylinder deactivation...not good.
The ford had the 5.4 three valve disasters on expeditions to around 2015.. crap... then ford went to twin turbo 3.5 eco boost.. and those can be bad.. still early to tell.

So i just bought a sequoia with the 4.7 v8 that can go a million miles. The 5 speed auto has a rep of lasting forever... but toyota had tundra and sequoia frame rust and breakage issues. So you need to be careful of that.

So it seems car makers are always having serious problems. You need to know what works and what does not.
I'm in the aircraft world. I believe that reliability is of paramount importance. Furthermore, there does not seem to be ANY performance penalty with good designs.

We can argue that Cessna's 172 has a relatively reliable, low powered, lawn mower engine for a powerplant. But that's cherry-picking the aircraft, the engine and the data.

From a "power to weight" perspective, and from a "fuel efficiency" standard, modern aircraft engines are excellent. The P+W engine in this pic makes 16,000HP and is expected to go about 10,000 hours before overhaul.

In this hypothetical, you are the head designer and engineer in charge of every major decision on a vehicle. Your resource allocation represents 100%. You have very talented teams of designers, R&D, developers, etc. But you have to allocate your resources between reliability versus performance.

Reliability would infer using a tried-and-true off-the-shelf product that has the bugs worked out, using more expensive and/or heavier stronger materials, perhaps less attractive or modern designs at times so some designs might suffer from appearing aged or dated.

For example, this category would represent the "best of the best" older designs, like the Jeep inline 4.0L, older Audi or Mercedes engines, the Ford 4.6L, or some of the famous Honda or Toyota engines, etc. and some of the best older transmissions, or other designs that worked well, heavier better quality materials (metals vs. plastics, thicker leather vs. pleather or thin leather, high quality plastic parts less prone to break, etc.) but are now dated and anemic by today's standards. Gradual improvements can be made here, to continually develop these older designs to make them ultra reliable and durable with incremental performance improvements. This category tends to give us 150-200 HP daily drivers cars and 250-300 HP trucks, but these older reliable vehicles seem to have a nostalgic lure in spite of anemic performance numbers.

On the other hand, Performance means pushing the limits, increasing horsepower or torque specs with new untested designs, changing the appearance of function to a new untested one, using new untested and often cheaper and weaker and lighter materials to save weight and cost (such as using plastic parts where aluminum or alloys were previously used), etc. This could represent the huge advances in engines and transmissions, etc. What we see in this category is modern cars that push incredible performance numbers with 300HP daily drivers and 600HP trucks and muscle cars, but seem to fall apart around year 10. The cheap plastics break, the paper thin leather seats and appointments wear through and tear off, etc.

What % of 100 would you allocate into each category? For me, personally, I am mostly nostaligic for the older designs that work, and would like my team to focus on making the most reliable and durable vehicle possible, with incremental improvements in performance. In other words, I place reliability as primary and performance as secondary. I would allocate my resources about 80/20 Reliability/Performance.

What about you?
Id go 60% reliability, 40% performance. The success of Jeep proves that many drivers dont care all that much about reliability.
As a Chrysler engineer, I would allocate zero points to reliability and performance, and instead instruct my staff to dedicate all of their efforts to dreaming up outlandish names for ridiculous colors in which we would paint iur vehicles.
Sinamon Stick takes the cake for that.

I’m still convinced “Destroyer Gray” is simply clear coated primer.
My Tacoma 2.7L is 100% reliability and 0% performance.

You need performance no matter how much you like reliability. Otherwise the vehicle becomes a chore to drive. I would give up 30% reliability for performance. If performance is any higher I’ll take it very fast and very unreliable. 90% performance 10% reliability. I don’t really see a purpose in 50/50 cars because it’s neither good at one or the other.
AS a business man, making the cars as the OP described, there has to be an evenly split factor in reliability VS performance. You need to make it reliable, but Fun, as well. With both fairly equal, you will enjoy it, it will get you where you need to go, and there is the built in obsolescence that will keep the customer coming back for another, and therefore, you in business. Too much reliability will get you a great reputation, but no sales. After all, Nothing broken, nothing needing to be replaced. All performance, gets too $$ to maintain and no one wants to buy. I vote an even split.
Reliability ranks 90-95% with me and performance 5-10%. Performance is no good if the car is sitting in a repair shop 90% of the time. I drove an '88 Ford Escort to 518K miles. It wasn't much of a performance car (1.9L 4 speed manual) but it was dead reliable and that's what I needed often driving 100-200 miles a day.
You are correct.. but the toyota and honda 4 cyl engines are close. The straight 6 ford 240 ci and 300 ci can go forever.

The toyota 4.7 v8 with timing belts can go a million miles and often has. The 5 speed toyota auto trans can run 15 years as well.. so there are cases of near perfect design that you can buy.
Toyota camrys and corollas get all the fame for being reliable, but the real ironman of toyotas lineups are their V8s, from the 1UZ till now. If you look at craigslist or fb marketplace you will routinely see multiple Lexus LS/GS400s from the 90s with 400k+ miles that still run fine. A buddy of mine had one with 440k miles years ago, we got it up to 150mph one night on a deserted highway. It was smooth as glass, like cruising at the speed limit, and this was on decrepit midwest asphalt. He wrapped it around a light pole in his neighborhood that winter unfortunately.
80% reliability 20% performance
I think the large majority of BITOG has high reliability expectations of vehicles, in general.
I would prefer to buy a commuter executed to 6 sigma reliability ( safety and drivetrain ) to 5,000 engine hours.
There are trucks designed and achieving that, but not commuter vehicles.
There are commuters that used to get to just shy of 6 sigma (w/ 5k), but I don't believe that's a pursuit anymore.
I believe that the bulk of these expectations, on the majority beyond BITOG, are shifting to lower and lower engine hours, trading for lower MSRP.
5000 hours is low. My Caprice has 65,000 miles on it and is sitting at 2300ish hours. There are 6.0 truck and cop engines seeing 20,000 before overhaul. Clinebarger has discussed working on 20,000 hour GM 6.0 truck engines. I know in Caprice land there are tons of old patrol cars running around with 10,000 to 15,000 engine hours.
Sinamon Stick takes the cake for that.

I’m still convinced “Destroyer Gray” is simply clear coated primer.
I thought about that 25 years ago when I repainted my Boat the primer color looked good when wet sanded and wet from washing off the sanding crud.
I think my goal would be 70/30 Reliability/Performance. But performance wouldn't be just speed IMO. Can be offroad capability, towing capability, fuel efficiency etc.

Just bought a 14' Jeep Grand Cherokee. Probably more like 50/50.