Go for 9.22 with the patch kit from http://www.os9forever.com

The Max RAM for that machine is 256 MB with two pieces of hard to find 128MB EDO RAM. The 6500 can take advantage of EDO.

A fast IDE hard drive will help speed things up a bit. Heck you could even use a flash hard drive.

With two PCI slots you could have a firewire/usb card and a video card in there.