For cold-weather riding in your regular cycling shoes, depends on how cold you are willing to go. I use a thin wool sock with my regular cycling shoes when the temps start to get cold. If it's windy, I add covers to diminish wind-chill on my toes. Once it gets cold enough to wear thick wool socks, I switch to a winter shoe that is a full size bigger. You should allow extra room for heavier-weight socks.