Flyer,
We have 2 of the ZD326 units with the 60" rear discharge. As gcmiller said above, there is not enough "lift" on the rear discharge decks, so the grass run over by the front tires does not get lifted back up and cut as short as the rest of the width.
When we bought our first one, we did not know about it. But like most things, you have to take the good with the bad. Mowing at a traditional cemetery, with lots of markers and monuments to mow along and around, the rear discharge was the main reason to get it. As for the scalping, after hitting the high spots long enough, they will either get cut down, or you can mow in a different direction to avoid them.
I have not heard how the newly designed decks work on the new 1XXX series mowers. Ask your dealer to deliver it to your place for a demonstration. That way you know how it works in your location, instead of the dealers yard.
As for the width and the power, you will have to determine that on your own property. The wider the better, in most instances. We have some tight spots where 60" can't go through, and then we have 5 acres of open ground that a 72" would be very nice to have. When the grass gets tall and heavy, we slow down on the ground speed while keeping the throttle high.
Digger