Shim,
I respectfully disagree with Zuki here, unless the difference that you have to pay is really small. After all the street price of the PA-800 is about two and a half times the price of the PA-500. I have had the PA-500 for over six months now and as regards what you get for your bucks I guess it cannot be beaten. Sure I would prefer a PA-800 myself but not for twice as much money. But then I do not put great store by things such as aftertouch, coloured screen, etc.etc. Do realise that though in essence the sound samples are identical, as well as structure and programming of styles, sounds etc. the PA-800 has the substantial added value of being able to load external samples.
Whichever way you go, you can now download my Musical Resources for free from my webpages:
http://pasounds.intropagina.nl/ and that goes for all PA owners of course.
Good luck,
John Smies
Holland