in my opinion the 6400/6500 wasn't a great Mac cause it's max amount of ram is 128mb which makes it very limited in what it could do (when compared to allot of other Mac's). if you run system 7 or Mac OS 8 then its not to bad of a system.

my friend has a G3 upgraded 6500 with a original radeon in it (it did play a few games well) and you seen a performance gain using the OS with the Radeon, but would crash allot due to lack or ram (if you ran to much at once or a game that took allot of ram).