I have a 717A, 48" 7Iron deck, with a 19hp Kaw. I do no mulching, but do use a chute blocker for leaf work in the Fall. In normal cutting, I use standard OEM hi-lift blades.
99% of the time, the 19hp is enough power. Only when I have a long upward slope do I sense I need to pull back a bit on the sticks. All my cutting is cool weather, northern grasses. Sometimes in the Spring, the growth is heavy, and wet. But, I don't find the 19hp a problem, only a bit of a challenge from time to time.
However, having said that, I wonder if a 22hp engine would burn less fuel. I get about 6.5 service hours, out of the 8 gallon full tank of gasoline (1.2 gal/hr). I think this is high on fuel usage. My 15hp Kohler Command Pro, single cylinder, driving my w/b will burn about 0.65 gal/hr.
In general, I do not run hard. Only in a very few instances am I running more than 70% full speed, usually about 4mph. My properties are too rough to run faster. I know I cannot control my machine like I want at faster speeds. My body thanks me for running slower than full speed.