I use the PI toe covers on my sidi lorica's all fall, and spring (like today for instance) I like them they allow me to stretch the season with those shoes which are my favorites and they provide just enough extra cover to keep the chill off and they can be left on the shoes with no fuss.
For really cold I wear PI Amfib covers and Sidi storm boots, they work pretty well. But honestly my feet are the only thing I just cant' keep warm enough when it gets below 0 F. I still ride but they get colder than I'd like.