To overclock today we relied on the Catalyst Control Center, no software fully supports this card yet, apart from the AMD reference package.
There was a huge amount of headroom on our review sample. We managed to push the core from 975mhz to a whopping 1,155mhz, almost 20% extra! The memory maxed out around 1,600mhz (6.4Gbps effective). Increasing the voltage didn't make a difference to the end result.
This significant overclock translated to a considerable 600 points increase in 3Dmark, scoring over 8,500 points. This is around 2,000 points more than the reference HD7870.