so stehts im Riva Tuner ReadMe:
Q: I've successfully unlocked 16 pixel pipelines on my GeForce 6800 and I don't see rendering artifacts in any games, however after unlocking that I'm experiencing problems with overclocking. Both RivaTuner and the driver's control panel refuse to increase core clock even by 1MHz. Can you fix this bug?
A: There is definitively nothing to fix, and I have to disappoint you: your mod is not successful. When you change the clocks, internal clock frequency stress testing is performed by the driver, and if you cannot increase the clocks even by 1MHz it can only mean that pixel / vertex units you have unlocked are not able to work properly even at default clocks. Some online tutorials advise you to disable stress testing with "DisableClockTest" registry entry, however I strictly don't recommend you to do it. Remember, that even if you don't see visual problems in your games after softmodding, the driver detected problems in their functionality during stress test. So I don't recommend you to fool yourself and hide the problem behind disabled stress testing. You can try to boost core voltage to make the problem disappear, but remember that this operation is extremely risky and can permanently damage your hardware.
Also auf deutsch gesagt, du kannst nicht übertakten, da irgendwelche vertex oder pixelpipelines nicht funktionst?chtig sind. Du kannst es ncht erhöhen, da die vs bzw. pp nicht mal bei Normaltakt fähig sind, richtig zu funktionieren.