Don't know about you, but -40 degs C or F is awfully darn cold. Very few places in the Lower-48 see those temps. OTOH, Interior and the North Slope of Alaska see those temps regularly, but not Anchorage area or SE Alaska. Portions of Canada see those temps, but they are not overly populated.
IMHO, 0W oils aptly apply in Fairbanks, while 5W oils apply in Anchorage and surrounding areas, to include most of the Lower-48 states (the exceptions being northern MN and ND). In Palmer, AK (55-miles northeast of Anchorage) I run QSFS (QSUD) 5W-30 in the winter. We see -32 and -33 degs F on occasion, though it's rare. I've made occasional forays into Interior Alaska and my LS engine Chevy truck has done well at -35 degs F on QSUD.
Keep in mind oils are allowed to slip a winter rating in service, so a 0w-xx can become a 5w-xx and a 5w-xx can become a 10w-xx. That's one of the reasons I am inclined toward oils with more PAO in the base oil blend, as they aren't reliant on PPD's to retain their cold temperature performance, meaning it is less likely to degrade in service.