I owned a fully loaded 9000 Pro and am very familiar with its shortcomings. However, the 9000 Pro is a far better instrument than the PSR 9000 and the only thing the PSR 9000 offers that the 9000 Pro doesn't is built in speakers. The 9000 Pro has better and more updated sounds, expansion card slots, more Polyphony, a superior feeling keyboard, 76 keys, expanded audio outputs, gooseneck lamp slots, and is built like a tank. For $800 its a no brainer, buy the 9000 Pro.

The 9000 Pro does have an underpowered CPU and if you load both Plug In expansion boards and sequence heavily with it, you will have some issues with the internal clock slowing down. If you don't do lots of sequencing you will probably never experience an issue. Given the fact you're getting the 9000 Pro for a steal, I think it's well worth the purchase especially at that price. My recommendation would be to make sure you load the final software revision Yamaha released as there were quite a few bugs in the earlier software.