Hello,
Haven't had that exact card, but I do have a Radeon HD 7850. Its the same architecture just a more mid-range card. While the RAM you can never know for certain, I'd say the core clock you can probably go higher. I run mine at 1175 MHz, but I've seen people pushing as high as 1300 MHz and higher. Just keep an eye on heat and give it a good stability test between each push and you should be fine to keep going. Oh and don't raise voltage too much. Might help stabilize things but thats the more risky setting to play with.