Well, last week it was -42 F, though today it warmed up to a balmy 4 F. Better find my trunks.
I run Mobil 1 0W-30 in winter and Mobil 1 10W-30 in summer. I agree the 0W-30 has a far superior MRV BPT (-58 F vs -42 F), but you have to trade that with a rather thin HTHS.
I worry about BPT as my 2000 GMC Sierra with Vortec 5.3 made knocking sounds from new. At -10 F, when the motor had on about 1,000km / 600mi, the factory-fill "low bidder" 5W-30 took about 15 secs to register oil pressure. Very sluggish pressure rise too.
The Vortec is a rear sump oil pan, with the oil pump mounted to the front of the crank. That makes for a VERY long oil pickup tube.
I hadn't quite broken in the motor yet, so I changed the oil to a conventional 5W-30 before some long trips. Still made that knocking noise, and at -20 F I parked it inside my heated shop. Why take chances??
When I had on 1,000mi / 1,600km, I figured the break-in was done and immediately changed to Mobil 1 0W-30. No more knock, instant oil pressure cold.
I think the GM Vortec truck motors are sensitive to BPT. Even if I am getting somewhat more wear running the 0W-30, I would be getting one h*** of a lot MORE wear with dry starts and KNOCK KNOCK KNOCK.