The extra weight of boots really make me tired and slow me down in the winter. Now I use wool socks and athletic shoes, and I drop a chemical handwarmer into the toe of each shoe. Works great. The temp the other day was 7 F and my feet did just fine. If I only ride for an hour or so I put the handwarmers into a baggie and save them for another short ride. If I'm going somewhere with the chance of getting my feet wet I take an extra pair of socks and an extra set of handwarmers.
I bought the handwarmers rather than the toe warmers because they seem to be a better value. This has made a big difference in my winter riding.