KTL, I live and hunt in southwestern Montana, and it gets pretty cold here. I've tried lots of sock combos, like you, and here's what works for me. I have a pair of boots from the Georgia Boot Co. They have a Goretex lining, and 600 grams of Thinsulate (I believe you can get much more than that). This boot is designed with a bigger box toe area, so there's built-in room for more socks without constricting circulation. (Some boots are just too tight to beef up your socks.) I have added an inner sole of additional Thinsulate. I use a pair of Acorn fleece socks. Sometimes I add silk or similar lining. Lately, I have been using foot warmers called Heat Treat. They come in the shape of an inner sole, and they work like the hand warmer packets that you break open and expose to oxygen to get them going. These keep going in my boots for at least 7 hours. I think it's imortant to ADD heat because no matter how much insulation you have, it seems like the cold eventually sinks in. The forecast for this weekend's elk hunt is 5 degrees for a high and -10 for a low. Even so, I'm not worried about cold feet with this set up.