For overclocking today we are using Sapphire's TriXX software.
We managed to push the card to 1,200mhz core from 1,050mhz and from 1,250mhz on the GDDR5 memory to 1,400mhz (5.6GBps effective). This translates to a 14.2% and 12% increase respectively.
The healthy overclock translates into around 700 points extra in 3DMark 11, pushing the Sapphire HD7870 FleX to just above the MSI R7950 Twin Frozr III.