Hello, I was wondering what you guys might think would be a safe overclock for a Xfx Radeon hd 6870 1gb. I have an aftermarket gpu cooler thats a Artickat twin turbo, when under stress on Assassins creed black flag i get around 52c in temp and was wanting to push some more frames out of it. I dont want to mess with the voltage on the card, so what would be best for stock voltage?