"Pour Point" is just a number thrown in to impress the guilable public. How do you define "pour point?"
Eg: A standard 1 litre beaker filled with Brand X chilled to -40 F for 48 hours. Tip the beaker on its side. How quickly must Brand X "pour" out to satisfy a "pour point?" 30 secs? 5 minutes?? So "pour point" isn't even part of the SAE J300 crank/pump test.
For cold cranking we have the standard CCS as defined by ASTM D5293. For most engines, CCS should NOT exceed 3,000-4,000 centiPoise, values that exceed this slow the starter down so much that most diesel engines won't spin fast enough to generate enough heat to fire the fuel.
CCS does NOT determine cold flow, and cold flow is far more important than CCS. An oil may be "thin" enough to allow cranking but be too thick to flow, so no oil pressure.
MRV as defined by ASTM D4684 has an absolute "yield stress" of 60,000 cP. Any MRV value approaching and/or exceeding this could result in no oil pressure or no oil flow in smaller oil galleries.
Most gasoline motors depend on "splash" to get oil on parts of the valvetrain and underneath the piston. Much thicker than 35,000-50,000 cP how can oil "splash?"
An engine sensitive to MRV values benefits from having an MRV value as low as possible, say 10,000-20,000 cP max. Of course there are always tradeoffs: usually an oil with good MRV values will have poor HTHS values, and vice versa.
Given the fact that you will experience MUCH increased wear, even failure, at temps -30 F and especially -40 F, you want first and foremost an oil with a very low MRV.
In pure town driving at temps colder than -30 F, especially approaching -40 F, the motor will never warm up. An oil at or near the MRV BPT will put heavy drag on the motor, so a little intuition should tell us this excess drag will have dramatic effects on fuel economy.
Don't forget the rest of the drivetrain. Automatic transmissions should not have a cold Brookfield viscosity exceeding 100 Poise. Most regular DexIII ATF's are at 100 Poise around -34 F, and most older Type F ATF's hit 100 Poise at -25 F. The torque converter will usually fail to transfer torque at +100 Poise.
By contrast, Mobil 1 ATF has a rated cold Brookfield of 51.5 Poise at -40 F. So we can see there will be MUCH less drag in an automatic at extreme cold temps.
Axles can have a lot of problems at cold Brookfield temps too. Empirical testing has shown that Brookfield's of 1,500 Poise allow "channeling" where the ball bearings in the pinion bearing and the ring gear cut a hole in the oil.
So everything runs dry, usually the pinion bearing fails first as it must support all the rotational torque. Then the R&P goes due to scoring/fretting on the teeth.
Something like Mobil MobilLube SHC 75W-90 has a rated cold Brookfield of 980 Poise at -40 F, with a rated "channel point" of -51 F.
With the cummulative effect of thick motor oil, ATF, and axle fluid, there are dramatic cold temp fuel economy differences.
Even running synthetics in my truck, at -40 F my highway MPG is never higher than 14.5. In straight town driving around 11 MPG. Friends with similar year trucks and motors get 11 MPG highway and 4-6 MPG town driving.
Of course, in sunny funny Phoenix, this is NEVER an issue.