We use EVGA Precision X to overclock our GTX 670. We set the card power target to 122% and fan at fixed 80%. Our review sample a maximum voltage setting to 1.162V. At this setting, we were able to overclock the card based speed to 1050 MHz from the default 915MHz. The Turbo clock that the card is able to achieve is 1202 MHz, a little bit lower than what we have seen with the reference GTX 670 (by about 40MHz). For the memory clock, we were able to achieve a 6.6GHz, a pretty healthy number for a GTX 670.
At this speed, the card consumes about 38 watts more power and with the 3DMark 11 Performance benchmark, we were able to achieve 14% gain, putting the card close to the GTX 680.