LOL! I have gear rated for -40, and usually don't break it out because it is still a little warm for it. Like you said, not sweating is the key, so that's my "real bad weather" gear for when it hits -30 or lower and is windy (and when isn't it windy, here?).
Layers are the key, and by the time I'm putting anything else on beyond the old M-65 with the liner in and a pair of insulated bibs, twenty below seems like a heat wave. As long as the outer shell stops the wind, and there's a little dead space in between it and me, I'm usually good. Oh, and I always wear a hat. By the time a little ice builds on the face fur, I'm pretty well good to go.
Yeah, I get all that... I am alright all the way down into -20 or so in my normal rig (Carhartt top and bottom) with differences being in the under layers... So long as I keep moving.
I have a set of woolies too, which work about the same so long as the wind ain't up... And I probably prefer them, though really use those only for hunting and woods, because they can't take work as well. I have an oversized light canvas shell for those, top and bottom, which I have turned tin for water and wind. But tins get heavy in the wearing, and don't breath well.
If it is much past -20 unless I am moving, I will probably be in my woolies, and the the parka, which is fur lined inside with a fur wind collar and face fur on the hood (the real deal)... And switched out to fur gaiters below the knees. I can sit in that rig, no matter how cold, all day long.
Cold as I been as I recall is proper -30s, but maybe colder up above the treeline (I wouldn't know), and some of that blizzard winds. I really don't mind down to -20, but somewhere around mid -20s I will start pining for a cabin and a warm fire. Normally that cold will see me busting out the feeding and hightailing for the house to hide by the fire with the womenfolks.
Unless I really get caught out, I ain't got to prove that no more, and cows/horses are generally more sensible than oil riggers. :D ... Except for cows calving, but thankfully they wait for freezing rain and slush on the ground, so they can get way up the mountain and into the thick brush, where they can find a creek to lay down in before they start having trouble. :|