You might look close at the Gravely 400 series. They go up to 72" and have carb., efi, and diesel option. The Kawasaki FX921v 31 hp is thirsty at approx 2.0 gph. I have a Kohler efi 28 on a Super Z and get closer to 1.2 gph, plenty of power though. IMO bang for the buck the Gravely 400 is hard to beat. Ask about the fleet discount of 20% off.
Rear discharge uses less hp. so better gph yet and you can trim with both sides of the deck. Down side would be you could never bag or mulch if desired later, also the clippings tend to be larger and not chopped up so fine as a side discharge passing them from blade to blade. Some what drops it like a sickle bar mower would.
For what your doing you could definitely do with a lot less mower IMO. More is better in my book too and will last longer and will get the job done faster but there are many guys using lesser mowers (such as JD 700s) to make a living and do well with them.
Ridin' Green may chime in he's got some seat time on the JDs