This is what I've had to do on long cold riders. Last month I did 25 miles (took over 2 hours) at temps between -5F and -10F, I had to dismount and walk about once an hour. I've read that feet don't get the same circulation pedaling that they do when walking.

I'm sure upgrading shoes would help, I use old hiking books for winter riding. I've lusted after some Wölvhammer, but I'm kinda cheap and that's a lot of money ($325)!

Also good sock and extra layers on the legs. I have a pair of "over the calf" SmartWool socks that are really good.