I've found most of the recent discussion here are aboutt newer keyboards as many members are working musicians with a preference for pro and top-end consumer models. Search for 'PSR' or 'PRS-500' (whatever) and select 'All open forums and archives' and you'll find a lot of information from previous years.

Specific questions are often answered by veteran members who have experience with older models - that's been a great deal of help to me. Also, Synthmania has some great write-ups and MP3 demos of older PSRs at http://www.synthmania.com/yamaha1.htm
Good luck!