If you have an Asus DirectCUII 7970 that happens to be Voltage locked please download the GPU-Tweak 188.8.131.52 software
Upon using this version of the software i was able to unlock my voltages, This was a true voltage option.
Before i could only get 1100Mhz before my GPU was unstable.
With the Unlock i can get 1.35V and 1275Mhz on the core and 1875 on the memory!
You can download the software here: http://www.overclockers.com/wp-content/uploads2/2012/10/GPUTweakVer2214.zip
Please let me know if this works for you, if not we can find a way !