Specifically the 6800 Go Ultra bios. Turns out that Dell has placed a lock on the card and so far RivaTuner and Coolbits fail to allow the card to overclock, it just resets it back to default anytime you try adjusting the clock.
nvflash is the utility that does the flashing. Try OmniExtremeFX for modding the BIOS. That will allow you to modify the GPU/mem voltage and set clock speeds.