Had to look up the conversion, so -20f is -29c, that's effing cold. I commute down to about -15c , -20c , and that's cold enough for me. Pretty similar basically to cross country skiing at the same temps and fat biking. I'll do it for a few hours, but it all day is a different kettle of fish-- and how fast the wind is makes a huge difference.
I've had derailleurs freeze up at these temps from road brine slush spray but usually you feel it coming so I get into a gear that will at least work when it happens

Have never winter camped, so hats off to the hardasses that do!