The 7300 does have a nice form factor, I would probably give that up if I were looking pretty specifically to build an OS 9 gaming system -- although I'm pretty much unsurprised by the listing of what you've got handy, so it may just be that Mac OS 9 games never really got to the level where they required the best possible OS 9 video card and the most possible horsepower.

But I'll also mention again I've done relatively little gaming, I just happened to see the thread and remember the discussion about powerful video cards for G4s.

It's also worth noting that I've always been of the mind that if you're doing something on pretty old systems, it's worth just upgrading to a newer system if you need more performance. (An attitude I've been trying to implement in my own stuff, but I definitely understand getting attached to a specific system or even a specific form factor or model.)