So looking at the CRB and then throwing in the sometimes quoted line from The Witchwar Legacy (which I do not have access to) regarding how any degree of energy resistance takes care of any non lethal damage, there is a conflict there of an at least attempted degree of realism. Consider the snow elf with 5pts of resist...could run around naked up to -39%. Ouch! This also means the trait in Reign of Winter could have that character skinny dipping in the ice flows with 2pts of resist...not sure that is the intention. While in some realms this might be kosher it is a bit extreme for me so I'm taking that as a resist to NON LETHAL as well as lethal. This would mean it would take lot longer for the non lethal to build up, and then when the lethal started kicking in that would take a much longer time as well. A tweak to the lethal damage rule instead of lumping it all together might be to say between 39 degrees and 0 degrees you take d4 instead of d6 to explain snow rompers, but I can see it working without that. Just because you live in a snowy environment doesn't mean you don't keep a fire in a cave at the ready, build huts here and there to warm up in, etc. . It just means less of you died off along the way as you built up an adaptive quality through natural selection and mutation...or the intervention of the gods of course!
A glimpse at some math-6htpt character=3 hours of failed saves getting 10.5 pts damage (average of 3.5 per hour)...almost doa by top of hour 4.
2pts resist you would be going strong until top of hour five when you started taking lethal and then you would last another 3 crawling through the snow till top of hour 8...
Opening up the numbers and assuming you take some damage with 5 resist you would take 1pt (the hour you rolled a 6, so to speak) per 6 hours...that is a lot of snowball fights! The same 6htpt character could rock and roll for a good day and a half till the damage started being lethal and then they could be ice fishing for another day till it started getting to be time to limp back to the igloo in your sandals and swimsuit....