In my car-less days of my 20s, I commuted 12 miles into Boston. One week I left the house at -5F every morning. Wasn't wearing any cycling clothes except perhaps shorts. Toeclips and LL Bean boots. Chopper mitts and liners. (I still use those for cold days. Very, very good riding gear as long as you ride a bike that can be operated with mittens.)

I rode a fix gear and recommend them highly for severe cold. Radically warmer going downhill. Any mittens work just fine. (Just stay away from slippery ones. Leather mitts can be treated with Snowseal and will be very grippy, allowing comfortable, secure handholds while keeping you hands relaxed, a plus for warmth.) Also ride cyclocross tires. They have two benefits re: warmth; reduced speed, hence less wind cooling and more work, hence more body heat. You also tend to crash less.

At 62, I am getting soft. And I get a lot colder now than i did when I was young. Probably circulation issues to my extremities and my engine isn't nearly what it once was.

Edit: just saw jd's post and remembered: sew-ups! Yup, I am serious. Cyclocross sew-ups. So when you have to change a tire, you just rip it off, stick on another and go. Less than 10 minutes, no brains required, no fine motor skills, no light required. (We are talking about winter, presumably pretty far north.) Get the tire on crooked? It doesn't care! And nobody's going to see it. Another plus - when you fall into that bottomless pothole - no flat and you can ride that wrecked rim home (and for the rest of the winter if you can stand the bumping!) This does assume you are riding aluminum sew-up rims, not carbon fiber. I can't speak for CF.

Ben