I just got one too, and thought there would be more headroom to OC. Did you unlock it or are turning up the bus speed? If it's the latter, like me, then many other things could be the cause like memory or any of the pci/agp devices that are holding us back. I am able to run Prime95 flawlessly at 141MHz, but no luck at 142MHz. I've turned up the voltage to the cpu and the memory, also turned down the memory timings from "Fastest" to "Faster" and from CAS2 to CAS2.5, but still no luck at anything over 141. This has started to make me think that one of my pci/agp devices is the cause.
Could be any of these for me: Voodoo5, SBlive!, Intel NIC, or STB TV tuner card