IS that the 800 with cache or without? I have a 2002 model 800Mhz with no cache and upgraded it to a 867 with 2MB and that was a decent upgrade in speed. My 2001 model has a 1.27Ghz 2MB cache Sonnet upgrade and it is fast for a single CPU (I use it in OS 9 mostly and some OSX 10.4.11).

I don't think you gain much from overclocking a G4. If you use OSX mostly then get a dual CPU (any speed) or just wait around for a cheap dual MDD (I have seen them for $140 complete and shipped on LEMswap) which will allow for 2GB of RAM. 3rd party G4 CPU upgradesd are still pricey compared to what a faster model G4 costs.