Factory recommendation is 42". Adjusted for things like altitude, what you are going to be cutting and its thickness / wetness, slope, what temperature you're gonna be operating at, etc....
I guess ..(actually, I know)…I was a bit crazy…when I had my 9N Ford (18 hp) pulling a 72” Rhino shredder.
It couldn’t LIFT it…. the shredder ran on its tailwheel …with the front chained-UP to the height I needed….. but I kept 27 ac’s mowed for 15 years with that setup…. until I could justify a Real Tractor (Kubota M4700).