Ztr's can take some serious abuse. I used to do some large sites with ours. The customers would leave the grass until it was knee dep sometimes and the ztr's could knock it down. Sometimes I had to make perpendicular passes to get things perfectly cut, but it beat buying another machine that I couldn't justify for the odd amount of times that happened.
Don't go ztr under 27 hp if you are going 60" or larger cutting deck. The bigger the better for horsepower. We have one ferris with suspension and a 34 hp Koehler. That thing is like a Cadillac compared to the exmarks. The price reflects the upgraded suspension though. If you aren't the one riding, then put a younger seasonal employee on an exmark and save the cash.