Let's see if I can answer first! ... They say you need 5 PTO HP per foot of rotary cutter. Give or take, maybe a little less HP per foot if you're cutting lighter stuff.
I run a 60 inch woods on my 3720. I am confident I could run a 72 inch, with the loader on for front weight. They get real heavy back there though. We had a 72 inch Woods on a Farmall 560. This is a fairly good size tractor, not a compact utility, and it made the 560 wheelie all over the place.
thanks guys...I guess I should have mentioned. I'm currently running a Frontier 60in with no problems. And seeking to go larger...72 and if I can an 84?? I never thought about the weight but it would seem to be a factor especially up and down hills.
I have a 96" woods DS96 pull type rotary mower. My 3720 cab has enough power to run it even when the air is on and pulling some pretty steep hills. I do understand that pull types are not great for everything. My dealer did say that the JD and the Woods 3pt 8' rotary mowers would be to heavy for my 3720.