Although I live on an island in the Gulf of Mexico nowadays, I've got 50 years of experience in the uber-cold Upper Midwest. It would help to know a couple of things:
1. How's the heater in your -4? Can you get the cockpit to, say, 50 degrees if it's 20 degrees outside? 60?
2. Are you thinking about off-field landing survival? Even if you survive an off-field landing, you may not be rescued for many hours -- even in Nebraska. The odds of freezing to death in January are good.
Just a couple of things to consider, before kicking off the discussion.