Around here if you don't want to have a realy short riding season you need to be prepared to ride in the cold. I draw the line at snow - if it's on the road I'm not. Last winter we rode down to about 15F at the start of a ride. I agree with the posters who say to start chilly. Whether I'm biking or running I'd rather be a bit chilly when I start than to be carrying stuff on the way back. That said at 20F I have been reasonably comfortable with a UA cold gear compression base layer, covered with a regular jersey, and a wind proof tight cyclying jacket. On the bottom I throw on a pair of UA compression briefs and a pair of Pearl Ozumi Pro Bibs, that are wind proof in the front. My cycling shoes with the bottom vents overed, with wool socks and shoe covers. For my hands I use silk glove liners in lobster gloves or in Hystra modified mittens. For the goard I just wear a skull cap under my helmit or a UA hood/mask.
I am thinking of adding a pair of Sidi Hydro's this year.