More importantly what motherboard do you have? If it's a VIA chipset, then the hard drives, video card, other PCI cards might not be liking the high bus speeds. Plus if you have a non-nForce2 chipset you won't be able to change the VDD, and it won't matter. But it's usually labeled "VDD" or "Chipset Voltage".

Also to rule the CPU as the culprit rome Prime95 for a bit or fold a protein or two, if that goes well then it's not the cpu. Upping the mem voltage a little would rule that out. Then if it's an non-NF2 board it's like that PCI cards/hard drive are not liking the high bus speed.