On my coldest commute, I left the house at -9F, not too bad so long as I didn't go much faster than 15mph, then the tops of my legs started to notice the added wind chill. Neoprene face mask & goggles kept my face happy. The ride home was brutal though. Winds came in, which warmed things up, but the headwind made for a much longer ride!

As a friend once said "There's no such thing as bad weather, just bad clothing choices" If I layer correctly, I can be pretty happy for a while down to about 0F, below that, I don't have good enough boots or gloves to be happy for long.