I haven't biked in weather that cold, but I have skied in colder. Wool is one part of the answer. The other is have big enough shoes. You have to be able to move your toes, even with wool socks on! The overbooties for windbreaking will help, but only if the shoes are big enough in the first place and you have wool for an insulating layer. It's entrapped air that keeps you warm, so the space for it and the fibres to trap it have to be there. The bike shoes that fit you in summer will be too tight for winter when you need wool socks. And if your shoes are too tight, your toes will freeze. When they hurt, that's a warning. When they stop hurting you're in real trouble! My son came home from skiing one day with boots half a size too small. His toes were dark blue. We had to take him straight to the hospital for thaw treatment (warm water) under sedation (because it hurts again as your toes thaw). Luckily, the damage was only temporary. Hopefully, he learned.