No one is able to tell you how far you can go, the best we can do is to give an idea of what other people have been able to get. You can start by downloading a overclocking utility, like coolbits, powerstrip or rivatuner all of these programs have a overclocking option. Just remenber that the cooler the card is the higher your oc will be, and if it gets to hot you'll se artifacts on the screen if that happens lower the oc by about 5mhz and try again, you can dowload ATitool to scan for artifacts for you, increase the clock slowly by about 5mhz at a time until ATitool finds artifacts.