When I did my over clocking on this card I was surprised to see that it didn't want to over clock to 580MHz. The highest I was able to over clock the GPU was a blazing 564MHZ. All of the 10 other 6600 GT's that have been through my PCI-E test box have over clocked to 580MHz with out any problem. Most likely the video card isn't being cooled properly. It could be that the AOpen 6600 GT's have a much lower yield than the others, but I doubt that is the case. Upon closer inspection of the heat sink, I found that AOpen chose to use very low quality heat sink paste that allowed the HSF to move, wobble, and do a dance with very little force. So I wiped off the white crap and dabbed on some of that fancy Arctic Silver 5. After applying the AS5, the card over clocked to 581MHz but no further due to the quality of the HSF. I believe a much higher clock speed could be obtained with an after market cooler.



Link: AMDZone