I really think staying up North for the winter is a total waste of time. I haven't been riding in 2 days - it's been below 30*, which is my threshold. Below 30*, I think you're asking for an injury. We've had some days in the high 50s and I noticed I rode better and was definitely less cranky. Maybe this makes me a whimp, but I see it as a matter of efficiency to prefer warmer weather for riding. I learned a long time ago that bearing adversity and training no matter what is a load of crap.