My problem is, I have size 15 feet, and am diabetic, with the attendant poor circulation and neuropathy of the feet. I thought my feet were somehow staying warmer as I got older, but I just can't feel them getting cold...not a good thing on a sub zero day!
I have tried liner socks under heavy wool, which did not do the job...ever, even in my X-county ski boots. They crowded my feet in my former boots, which I thought should be 13-14s.
I now have some Cabela's Iron Ridge boots,1000gr. insulation, and wear a heavy pair of wool socks with them. Plenty of room, and my feet seem to stay very warm. Maybe not the best, but they are what I can afford, and come in my size, which is no small thing. No pun intended.
I have a pair of Browning boot socks, and another pair of Smartwool socks, which are very heavy, and my size, that I will be trying out this winter.