I think extended high speed operation is the easiest thing you could do with that engine. It's a Jeep, not a Ferrari. It's got the aero of a barn door. It can cruise all day at 90mph, but at 12mpg. It's governed at 99mph top end and could run there all day, too. Nobody wants to do that it a Jeep. It is not DI, nor does it have forced induction. It is VERY easy on oil. My wife idles hers for long periods (drives me nuts) and it hasn't shown any sign of fuel dilution.
I've driven twice to Moab (22-23 hours each way), to Maine, and to Florida and back, 75-90mph and sometimes against strong headwinds for much of the way. It never broke a sweat on 0w20.
Instead of an oil with a bunch of VI in it to stretch it from 0 to 30, I like Mobil 1 EP 0w20. It has mostly PAO base oil and will handle that kind of life very well. Plus, in Germany, there's a great selection of high quality 0w20's.
This engine is NOT hard on oil. It is doesn't have DI or forced induction. I've run OCI's out to 8k miles with a mix of long highway runs, hours upon hours of rock crawling in 100 degree temps, (AC on the whole time) and VERY dusty conditions. So dusty that I changed the air filter before the drive home. The UOA came back with the oil still in great condition. I have done most of those trips on Mobil 1 EP. The trip to Maine, which included both long highway runs and days of 0ff-road crawling, was done on Shell Rotella Gas Truck, which I don't belive is as stout, but it handled it with ease and showed very well on the UOA.
I'm in 3 Jeep clubs and we've got a number of gen 1 Pentastars achieving the 300k mark with no issues beyond good maintenance. Most have done it on 5w20 and used the OLM for OCI's, which put them between 7500 and 9000 miles. I'd say the most popular combo is Valvoline Advanced Synthetic and Mopar oil filters. But they all have their favorite oils by which they swear.
There is just no reason to break a sweat over oil weight on these things. Just run a good quality 0w20 with a brand that gives you confidence. They are built to last a long time, even if giving them a royal beating off-road every now and then.
By the way, @OIL_UDDER advises that you mash the gas frequently on these things and get them to high rpm. He said the oil in the valve stems will evaporate out if you drive like a granny for long distances and many hours. Running it hard splashes oil up in there. So the harder you run them the better off they are. That'll be far more important than sweating over viscosity. He should know. He designed the Gen 1 Pentastar.