Need more detail about tractor. 2wd or 4wd? Gear or HST? R1, R4, or Turf tires? Loader, weights, fluid in tires? HP shouldn't be a problem as long as you watch your ground speed vs brush/ grass height.
I have a 1300lb JD390 behind a 70hp AGCO Allis 5670 4wd with no issue. Also have a 700lb JD25A behind a JD4300 4wd HST with no issues on our TN hill farm 200' hill on 48 acres. All our tractors are on R1 Ag tires that are fluid filled with Rimgard. Keep the loader on the JD4300, but take it off the 5670. There are a few ravines that we need to be careful around, but that's true regardless of what is behind the tractor. I need to widen the track of the 5670 to be more comfortable on the side hill above our pond, but for now we just cut this area with the JD4300. I do the majority of the mowing with the AA5670 and usually cut 4' grass/brambles in M2 (3.2 mph). But if higher or thick Johnson grass i drop to M1 or L4. I mainly watch the output of the cut and slow when i start seeing stalks.