Here's an article I quoted from guru3D.com
"Yes, we can use Rivatuner to unlock that extra quad and enable that lost vertex processor also. Now here's what you need to bare in mind: that's opening Pandora's box right there as it's like a casino slot in Las Vegas, you need a bit of luck. See the extra quad or vertex processor usually is disabled as it's defective. That's how it works in this business, if it passes all tests it'll work as a (6800) GT or Ultra, if it has a damaged quad it'll become a GS or standard 6800 or whatever NVIDIA decides to do with the chip. So it's all about yields but often the vertex unit or extra quad still works, perhaps not both. You could be lucky and there's no harm in trying."
It's more of a gamble now isn't it.