Truei don't know that i would base that solely on tractor hp. tractor weight is going to play a bigger role in handling the weight of a round bale. i have 2 other guys in my hunting lease with higher hp kubota tractors that are less capable at certain tasks because they can't put the hp to the ground. one has a 65 hp that weights in right at 2k lbs lighter than mine. so while he may run a bush hog at a faster cutting rate than i can. he cannot pull the disc i can nor was it as capable with a grapple due to the lower lifting capacity of the loader.
And utility tractors are gonna be heavier pound for pound than a CUT
But still a utility tractor heavy enough to lift a 1200lb round bale with the fel safely and move around is gonna be 55-65 hp