Sapphire Toxic HD 5970 4GB Review
 

To put it bluntly, this is the fastest, out of the box video card I have tested. The fact that you can run these clock speeds on a card of this stature with 4GB of memory is pretty amazing. With a small bump in voltage to the cores, I was able to reach 1000MHz without a sweat. I just wish I could have pushed further. Even AMD GPU OC Tool did not give me any love, so 100MHz worth of improvement on the cores is the highest benchmark stable clock speed I could pull from the cores.

http://www.overclockersclub.com/revi..._toxic_hd5970/