No, I'm not a professional landscaper but we do have a ZTR to maintain our 2 acre property that our business is located on.
A few months ago we bought an Exmark Quest S-Series 42'' ZTR and have put 13 hours or so on it so far. It's a fantastic machine, such an upgrade from our old Snapper rear engine rider - I actually can't hardly use that thing anymore because it feels so powerless!
The Kawasaki FR691V is a monster, I honestly don't know why you actually NEED 23 horsepower on a 42'' cut mower, but I like it! Never any major bogging or stalling, ever, even in grass that's a foot+ tall.
Although the Exmark is a great machine, we could've bought almost the identical mower from a different dealer (Hustler Raptor) for $2799 instead of the $3799 for the Exmark (Exmark was on sale for $300 off, too). I'm glad though that we got the Exmark because our dealer is like the best around in my opinion.
We could definitely go with Exmark again, but I'm sure we won't have to get another new mower for a long time since we take care of our equipment and keep it going for as long as possible.