You really have to ask, "What was your coldest commute and how long was it?" You might ride for five miles at -10F, but would you want to go 25 at that temp? My commute is 12 miles and the coldest ride I've done was 7F. I won't do that again. I have two long hills to come down and thought my eyeballs would freeze me blind, ha! I rode at 11F last week just because I had been off the bike for too long due to injury. Generally I'm comfortable down to 20 for that ride.