Depends on what cooler you have on the card, but the best you can really hope for is a 10-15% overclock. You might get it to 950MHz on the core, and 1300Mhz on the memory, but don't try much higher. Slide to those settings in CCC and see if you get artifacts in games. If so, or if the card cuts itself off and then back on (don't panic - it's a safety feature - takes a minute or two) then lower the clocks by 10MHz and try again.