Just an after-the-fact FYI...
Ratings are all over the place with cutters. Basically it comes down to, as emphasized here, weight, but also HP rating of gearbox.
I ran with a "light-duty" 60" Rankin off my Kubota
B7800 doing some of the most nasty stuff one can do with one of these things and it held up pretty darn well. That said, I replaced it with a severely used Landpride 1860 (I believe), which is more "medium duty," and have found it to be a lot more robust (I wince less about running over crap). The Landpride's quick attach was what I was wanting:
B7800's lower link arms are really a pain to adjust- quicker to just slide pins in than hooking the arms over pins.
My commercially abused BH26 on my NX is another beast. This one is a true medium duty cutter, but it was reinforced, in which case it's closer to heavy duty. Any heavier duty, and using it as such, and I don't think I'd want to be around it when operating: the noise of it chomping on stuff is intense- having a cabbed tractor is another plus here.
All said, I have had good results with buying used (and in a couple of cases extremely used) cutters. Have probably about $1,100 in the Brush Hog cutter; a new one would be close to $3k; my brush can't tell the difference!