I don't know about the models of this brand,general rule is 25 hp for 5 ft cutter,30 hp for 6 foot cutter[5hp per foot].
You could use a 6foot on that 32hp probably no problem,but wouldn't think anything bigger.[also depends on pto hp as opposed to engine hp],depends on weight of tractor,etc.
So if above is correct than 40 -45 hp for 8 foot cutter
On the other hand my ck30 kioti's book says it has 23 pto hp,I use a 5 foot cutter and pretty sure I would have no trouble with a 6 foot cutter,even in tall heavy grass.
Another thought would be weight of a big cutter,[not sure how big the three point lift ones go up to],the bigger ones are just a pull type,and how narrow a place you can get a bigger one through.