I've bought a used gigabyte 7970 ghz edition off ebay and have the feeling there's something wrong with the product.
It's meant to have 1100 mhz GPU clock and 6000 mhz memory clock out of the box but GPU Tweat and Catalyst Control Centre and showing speeds of 100 0mhz and 5500 mhz.
You got scammed hard! Haha no just kidding, check the GPU with GPU-Z, free downloadable utility, just google it, and it will tell you what card it is. Even if it is 7970 instead of 7970 ghz, doesn't matter just have to overclock yourself.