I hunt South Dakota in the winters and I seem to do fine with a 400 gram insulated boot... I count on my socks to provide the insulation. Layer one pair thin nylon/polyester/spandex socks and one pair heavy wools over those... that way I can use the same pair of boots all season.
Currently using these:
http://www.cabelas.com/product/Footw...3Bcat104841180