Edit for the above post.
Using my 460 with the 920v I'v been cutting here already and I'm starting short at the 2" mark. First off I'll say this is not my norm. We've had more thatch here than normal due to a mild winter I guess. I cut a golf course property that the owner decided against having dethatched this spring and it has a slight grade to it. Even though I took my properties back to about 2.25" this fall they grew from late fall to early winter here by about an 1" to 1.5" on the average. The combination of the deck being this low (dragging ant-iscalp wheels and possibly the nose of the deck in the grass), the slight incline, and the thatch and grass combination it really pulled the engine rpms down like I never thought it would. Other than using too much fuel even when cutting in normal conditions I am glad I did not go with a smaller engine. And I haven't even installed the bagger yet to see how much it will pull from it. The more hp the merrier IMO. I'd love to try the new BB Kohler EFI and see how it does in gph and hp.
Regarding my previous statement on JD I'm in the market for another mower and have been looking at the 960r and found they now offer flex forks along with a suspension seat so they finally stepped up their ride. Trying to set up a 960r and Super Z HD demo in next week or so. May also be looking at Cheetah and Exmark X RED.