Also with a 73hp tractor if it was properly weighted you could pull a 18ft disk on flat ground, 14ft and below for sure. That would prob mean lots of weight and maybe duals to run at a decent speed on the bigger disks, depends on the angle of cut, dual disks, size of disk blades and the concave angle of the blades ext.
A 6ft disk on a 75 HP tractor would be laughable lol.
as far as the 75hp tractor being too big for the 7ft cutter? My thoughts is as long as the PTO spins at 540 you should be ok.
I could see where the extra HP might damage the cutter if the shear bolt or clutch fails and it's a 75hp engine vs a small tree with a metal cutter blade in between. Like Scotty said, you don't have to run full throttle. At full throttle you burning a lot more fuel anyway.
After doing some research the 5055E and 5075E look to be the exact same tractor other than the 5075e it turned up more, 23 more HP and 40 lb-ft more torque looks like. All the lift capacity ext is the same on both. You would gain 16 PTO HP going with the 5075. The tractors even weigh the same.
It's interesting that that line of tractor has a 2.9L 3 cylinder and mine has a 2.4L 4 cylinder, both are turbocharged.