Once you get used to the Exmark you'll never use the SD Ferris again. The only advantage the Ferris has over the Exmark is instant reverse. Well, that and a better cut. The belt drive Exmark is easier to turn and can be easily used on hillsides.
I have a Ferris 36" SD and we're finishing up putting steering brakes on it. Then I'll be able to use a sulky on it and do hills.