Ok, I'am quite sure I miss something but can't figure out what. I just moved to a new case and would like to start OC'ing the 8800 a bit. I've opened RivaTuner -> Driver Settings -> System settings -> check the OC option -> performance 3D mode. Now when I move the bars the "Test" button below should become clickable if I remember correctly. I can click apply with the moved bars (520/800) but nothing happens, the monitoring still shows standard clock speeds (513/792). Using ForceWare 158.45, Vista 32bit, uninstalling/reinstalling driver/RivaTuner did not help, any suggestions? Dynamic fan profiles are working by the way.
I have XP not Vista. Here, it's normal what you describe seeing that xp is 2d and you are oc'ing the 3d mode. To check if you are doing everything ok can you underclock the card a good 50 mhz and see if that works? And if yes try to o/c more than 8 mhz, you can't set the clock on the g80 from mhz to mhz exactly.
I've set it to 530/810 and it works now, thanks guys. It is a bit confusing though that you can't set the clock speeds exactly.