The older chips like that were so much harder to overlock. Since the "K" series of Intel and the "FX" series of AMD where they give unlocked multipliers, it's so much easier to overclock and find a good balance between a simple multiplier overclock and FSB overclock. On your chip, all you can do is increase FSB, which increases the speed at which RAM, PCI express, everything runs and usually limits how much you can overclock as older systems like that don't take a huge FSB increase.
This generation of intel or amd's, easily a 500mhz overclock on just about any "K"/"FX" chip, even on stock without touching the bus or voltages.