I'm not an expert in this field, but I know that having a good pair of wool blended socks are just as important as the boots you wear around them. I think most "cold feet" are caused from sweat and the inability of a-lot of socks to draw the moisture away from your skin. I wear 800 gram LaCrosse rubber boots and a good pair of wool blended socks, and if I don't have to walk a mile to get to my stand, my feet stay fairly comfortable. Make sure your foot isn't too tight inside your boot, giving it a little room to breathe, and stay away from cotton pairs of socks. It isn't a terrible idea to also give your bare feet a quick coating of anti-persperant to help keep them from sweating in the first place. Hope this helps a little.
CRITR