Last weekend I was in Kansas for a late season deer hunt and my feet froze in temps that were -9 with the windchill included. I was wearing 1,000gram thinsulate boots with heavy Bass Pro socks while in a Heater Body Suit and my feet still froze. So now I'm thinking I might need a PAC boot to keep my feet warm for next year. What specs should I be looking for in one since there are so many choices and options. Thank you.