Alexey Nikolaychuk, the author of RivaTuner, has found the mechanism, which NVIDIA cards use to set 12 or 16 pipelines on GeForce 6800 and 6800GT/Ultra, respectively. Of course, if a card has 4 offline pipelines defective, it will produce artefacts and we can't guarantee that any GeForce 6800 can be remade into a 6800GT.