Catrin, I think the lowest temperature I have ridden in with the combo of road shoes, wool socks, booties, and chemical warmers was close to 32 or so. In fact, there was one morning about a month ago that Hirakukibou and i had a planned ride for 6 AM; it was about 33, even though it was still September. We were determined not to bail, and that is the combo I had on my feet. I may have ridden in the 20's, but it would have been nothing more than a 10-15 mile ride on my old hybrid on a sunny day in February.
I also have the Seal Skin socks, which I bought for a tour. They are *extremely* warm, but somewhat a pain to get on/off. I bought them mostly for the waterproof aspect and I have worn them hiking, too.