How much power needed a 6' mower?

I run a six foot Caroni finish mower behind a 21hp Iseki TU180 with power to spare. Really beats the heck out of my Simplicity with a 44 inch deck! Rides over the bumpy areas much better too!
Nick

Thanks - I thought that might be the case.. I'll have to find something smaller. That model was the smallest the manufacturer offered with the side arm. I'll ask for suggestions on cutting under fences.