For those who enjoy the Mukluks, and wish to increase the warmth and provide a little margin of grace should one step through a beaver run or drop into overflow, try putting a pair of neopreme socks over your wool socks.
This, in effect, creates a vapor barrier keeping the wool liner dry for extended periods of dry cold, and provides a waterproof barrier in the event of a dunking.
Of course, everythig is a trade off. Using a neopreme sock keeps the moisture against the foot, trapped in the wool sock underlayer. Much like wearing a pair of the old MickeyMouse boots (technically a vapor barrier boot) you have to be prepared to switch socks at mid-day. This is not so critical on a one day outing, but for extended trips, the danger of developing trench foot arrises. Simple to prevent with prior planning.
I have been outside the greater part of today with the temps hovering about minus 28 and my feet have been quite comfortable.
For extreem conditions get the mukluks oversized enough to provied room for TWO felt insoles along with the felt boot liner.
The mukluks ability to breath makes it so much warmer than a typical sorrel type boot (with the rubber boot bottom) that there is no comparison, especially if one finds oneself going in and out alot. The moisture trapped against the rubber (or heavy leather for that matter) turns to ice in short order, negating any possiblity of the body heat ever drying it to the point that insulative value is restored.
Just my experience in keeping my toes warm in a frigid environment.