Nothing like deciding to extend your ride by 10 miles because you feel so great (due to riding with a 20mph tailwind) only to turn around and realize you're about to average 10mph less on the way home because of the wind. Ugh. I prefer to ride into the wind to start as it's always more satisfying to end a ride with a tailwind IME. As to wind chills, I don't feel that much of a difference between 25F and 0F. At those temps, the only skin I have exposed is my nose (otherwise I fog my glasses immediately which then turns to frost). My toes my get cold a little quick though. I did 60 commuting miles over the past two days with windchills between 9F and 20F (temps between 24F and 32F). Great cycling weather, provided you have the right clothing.