Ferris is600/700 both have ZT3400's. FS series engines though. To go to FX engines takes the mower cost up another $1-1.5k usually.
The Kawa FS series engine is more than enough engine for a 1.5 acre yard for years and years of service.....you should be able to get 1000 hours out of one easily. The FX series is a 2000+ hour engine. Like a diesel, for most home owners, it is overkill.
My deal with big dog mowers, is look around, name a LCO company that uses them.......few if any. Stick with what the commercial guys do, there is a reason they like/use the Scag/Gravely/Hustler/Toro/Exmark/Ferris's.