Yes, you can OC you're GPU, OCing your GPU is typically done through software in your computer and not through BIOS.. So its fairly safe, and easy to OC your GPU rather than you're CPU.. When OCing, I would increase the core clock or memclock in 50mhz notches, only increasing a notch each time.. but to test if the OC worked after you turn it up a notch.. Load up a game and start playing and if it allows you to play the game(actual gameplay) if it works, you can try bumping it up another notch.. IF it doesnt work, you can also bump up the power usage.. by just a notch or a couple percent( 3%) depends what kinda of software you're using..
Keep me posted with any questions! IF this helped click the solution button!
Cheers!