What I gave was only an example and is all relative, if you need to slow down a certain percentage to do a satisfactory job with a 72" deck, you must also slow down (possibly more) to do an equal job with a 104" deck. There is not enough hp offered with the 104 to keep it at full rpm while mowing grass with any moisture or thickness, much less mulch with any speed relative to productivity. To mulch with an 8.67" deck and do a reasonable job, you will need a 45+ hp engine, you need a strong 40+ hp to side discharge and maintain relative rpm's. Toro calculates 5.5 to 6 diesel hp per foot of deck width on their wide area mowers. I run a 35 hp Kawasaki on a 72" Super Z, and believe me it needs every hp in average cutting. So for a person to believe Hustler is offering enough engine hp to adequately pull a deck that is over 2.5' wider is ridiculous. The 38 hp Kohler is no stronger than the 35 Kawasaki, it is relative to each companies standard of hp rating, and Kawasaki's rating method is much more accurate than that of Kohler's.