I have shot on several occasions for several weeks at a time in Yellowstone in winter in temps from 0F down to minus 30F, carrying my tripod exposed on a snomobile or the roof of a snowcoach.
Carbon fiber is the best. In addition to light weight, it just does not get cold to the touch like aluminum and, in the event you bare skin touches it, you will not become permanent siamese twins!
I suggest looking for used Gitzo. I have a model 1325, which is heavy enough for basically all 35mm and 645 set-ups with the right head.
I have never seen, or heard, about any failures of carbon fiber tripod legs at these low temperatures. Maybe some cheap ones?? You are right, though, that brands with plastic knobs, lever leg locks, etc, might have an issue with the plastic fittings becoming brittle.
That's why I like Gitzo, its rotating rubber locks are very large and easy to use with gloves, and I have never heard of them failing. The legs do get stiffer in extending or retracting ins such cold, but the rotating locks open up quite a bit and my tripod has always been useable. Lever leg locks cannot adjust to the same degree. One person I know did have an issue with taking the tripod into his room after shooting in deep snow, and the snow melted and when he went outside again it froze up and the leg would not move, but that is not really an issue with the tripod.
For your specialized use, I agree with avoiding Manfrotto carbon fiber due to the fittings, not the legs themselves (I use a manfrotto CF in all sorts of moderate conditions with very great ease).
Gitzos are not cheap. I think Slik makes a CF tripod with rotating leg locks similar to Gitzo, and maybe other brands as well.
Guy