I have had my PIII 500E on a Soyo 6ba+ IV up to 775 rock solid...no problems but I bought a new video card that complained badly about being o/c 'ed that high.
128 mb generic RAM
13GB IBM deskstar
Diamond MX400 sound
Rage Fury MAXX agp
o/c was with 16MB ATI Xpert128 pci