Yes, hills near water are crazy dangerous! Reason is you lose control, flip into the water and get pinned and drown. This very thing happened to a coworker's husband last summer at Pleasant Valley golf course in Iowa City. Very sad. Nice guy with a couple kids.
Yes there's a lot of good machines out there but what no one has discussed is the transmission. The two main choices are a transaxle(one expensive unit) or a pump and motor for each wheel. The transaxles are fine for flat, but if you're doing hills or several acres, you have to size them properly or they overheat and burn up. They're also a bit more difficult to precision control.
For me, I'd never own a transaxle. A bit more expensive but for what you're wanting to do, I think you want wheel pumps and wheel motors (one pump and motor for each side). I set mine up for speed with 15cc Hydrogear pumps and 12cc Hydrogear wheel motors. Aggressive 26 inch tires and I'm mowing at 15mph. Should also note that Parker also makes a high quality wheel motor and pump. Hydrogear and Parker. Don't even look at anything else.
Yeah my mower is fast, but if I stop on a severely steep hill, I don't have the torque to easily move again. If you're doing steep hills, 10 or 12cc pumps with 24 inch tires is the way to go.
Someone mentioned horsepower. Horsepower ratings can be very deceiving. I bought a Briggs Cyclonic 30hp engine a few years back. It was a turd. I then bought a Kawasaki 850 27hp and wow what a difference. I can't remember the exact specs, but the Kaw was outperforming in ft lbs of torque. That is the important number, not the horse power.
The big three are Scag, Hustler, and ExMark...and Bobcat is really making a great machine now also. All great machines. But if I had Daver's money, I'm buying the Ferris with the 4 wheel suspension. You cannot beat the comfort ride of that machine! I'd even bet if he get's one he'll turn it into a mobile ground blind
