go into settings and unlock voltage control then peg out the voltage slider. start with adding 100mhz to the core clock then start moving up 13mhz at a time and testing for stability by looping the unigine heaven or valley benchmark. eventually you will start seeing artifacts then you will want to back down 39mhz or so and leave it there. if your card starts passing 79-82c its likely to start throttling which you don't want. keep the card under 80c.