So, I picked up some toasty feet, and today I got to ride in ~ -5F temperatures for only about 15min. Which isn't long, but for commuting purposes I can get pretty much anywhere in my town in about 15min, and -5 is about the coldest it has gotten in quite a few years.

So toasty feet = quite effective.

(although I haven't yet had a chance to test them with just standing in the snow, and I could tell that my feet were beginning to cool off when I'd gotten to my destination)