Lemme see if I can remember this right... :-D
The PowerMac 9500 was originally shipped with a powerful 604-chip rangeing from 133mhz upto 233. This baby (the mac) accepts cpu-cards, so you can upgrade the processor with an accelerator from for example
Power Logix.
Apple has never been to friendly with standards and so the 9500
doesn't use a regular AT/ATX power-supply. My G3 uses some custom thingy.
If you ARE going to buy these babies I have one tip for you;
BeOS.
BeOS runs natively on these Macs and can be quite the fun OS to play with.
As for Mac OS'es the 9500 should be able to run everything upto Jaguar, although everything after OS 10 will be dead slow...
I'd say the lot is worth around 100£ give or take...
But that's money well spent for a new hobby... ;-)