[MacDoc]

The AGP cards will make a substantial difference in your X performance.
The video card will take the processing load off your already limited chip.
There are some nice processor speed bumps for your box now too.

We've got some 32 meg GeForce 4mx that are very quick in X and reasonably priced trade ups.

 

[MacDoc]

There were two version of 350 G4s - Yikes and Sawtooth - Sawtooth are rare but around.
They are quiet and very upgradeable both video and now processor.