Correct me, if I am wrong, but most of the finish mowers that I have seen are 4 wheeled. So, the tractor is not supporting anything.
Additionally, I have seen several 60" finishing decks that claim to need only a 15 HP tractor.
I still am looking at the 38" deck, primarily to cut the ditch bank along the state road. The ditch is easy to walk along, just a bit too steep to drive a CUT.
Is there a trick to measuring the angle of a ditch bank? Coach Doheny was my Geometry and Trig teacher in high school. I could brush off the cobwebs and calculate the complementary angle of a right triangle.
(Math was great, especially during football season!)