For moderate weather (down to0 F) I can wear Army wool/nylon inner and a medium weight wool or polypropolene outer with 800 to 1000 gram Thinsulate, Goretex leather boot. Important never to make the feet with sock too tight in boots. That's a sure recipe for cold feet if you do.

For colder weather (sub zero to 25 below) I wear either the best mohair socks in 1000 gram thinsulate Gore-tex boots. They are very warm, soft and keep my feet warm. They naturally wick sweat away to keep feet drier and warmer.

This is where I get my mohair socks. "The goat Lady" near Harmony MN. I'm sure there are others who make / sell them. I like this lady's spunk and her socks her stay at home moms make out of mohair she grows on a couple hundred of these goats.
http://www.woolworks.org/stores/mn.html