In the 1960s or early 1970s the meat lab at the University of Wyoming weighed a large number of all kinds of game animals, hog dressed(whole with the lower legs, hide and head off), and found for elk that branch-antlered bulls averaged about 550 pounds, adult cows 450 pounds, spike bulls 350 pounds and calves 250 pounds. While the numbers weren't exactly 450, and so on, the differences weren't much. So, Utah Lefty is pretty much on the mark, based on measured hog-dressed weights and tossing in the weight of the skull, hide, lower legs, and innards. Anything bigger is probably being fed or frequenting something like an alfalfa field.
