I have a sapphire 7970 non-ghz edition that I had to modify the bios in order to unlock higher clock speeds. It is currently running at 1175 core and 1700 Memclock. I am getting about 306H/s with this settings. If you settings max out at 1545 something on the memclock you will need to reflash your bios with, I think it was the vapor-x 7970 bios. That allowed me to use higher clock settings.