I OCing my 660 use Afterburner hour ago. Voltage control is locked so i just max the power limit slider to 110% and next add little 20MHz to my core clock. GPU-Z shown that my core clock rise but when i run Kombustor the clock while running become slower! The clock running between 960-980 (default clock 998MHz ). I just try everything, rechange core clock, change the memory clock, change fan speed, rechange power limit, and it was still slower. But i don't know what am i did now the clock became faster, it run in 1078MHz. Phew, thats weird. Anyone can explain this? Thanks in advance
Your gpu is throttling. My old 560ti had this same issue. It would constantly lower even when the temps weren't that high. I never found a fix while I had the card. But here is one that seems like it could work.