Asus Hd 6970
 

Overclocking the ASUS HD 6970 wasn't the easiest thing in the world to do, but it wasn't all that hard either. I first started out using ASUS Smart Doctor, however, whenever I tried to push the core clock past 940MHz, Smart Doctor would automatically reset it. After I encountered this problem I decided to switch over to MSI's Afterburner. After increasing the overclocking range in Afterburner's config file, I was able to continue overclocking the ASUS HD 6970's core past 940Mhz. That being said, I encountered another problem. MSI's Afterburner would not allow me to adjust the card's voltage. I eventually decided to use Afterburner anyway and ended up with a core clock of 986Mhz. This was about 100Mhz above the factory clock speed, so I was OK with it. I got a lot nicer overclock out of the memory, which ended up clocking in at 1502Mhz.

http://www.overclockersclub.com/reviews/asus_hd_6970/