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