James Bond wrote:
I suspect that the overclocked PCIe bus might be at the root of this
problem. Maybe the graphics card is sensitive to the overclocked frequency.
Or maybe the SATA disks cannot handle it.

No I don't think PCI is causing your problems but even if PCI buses are
guilty you can always lock them with some OCing software.
I believe that your problems come from the SATA disks,they hate OCed
FSBs and high voltages.