I have two choices, I have a pair of Pearl Izumi Amfib tights that I wore in the 40 degree rain we had here, and I ride fixed gear all winter. I also have a pair of Bellweather tights with windstop nylon on the front side with a knee joint, they are toasty and I am good to -23F last year, of course the bike wasn't that night my Surly hub imploded, something about how I'd set up the cone nuts, and tightened the axel nuts. Man that was a night from H E double toothpicks. I did manage to ride in -4F my 24 mile commute, and was mildly hypothermic last year. I was cold and clamy by the time I got home, had stopped sweating and couldn't warm up. Scared the buh-gee-zus out of me. I jumped in the shower. later learned that hydration is just as important in the winter as in the summer. I'd not drank the whole ride, or had stopped cause the water bottles were frozen. Add to that the breathing in cold air brought my core temp down, well... I had images of being found like the old geezer in the movie "Jeremiah Johnson," frozen with my rifle still in my hands.