NVIDIA GTX 670 Review @ OCC
 

The GTX 670, when run at the default speed setting, showed a nice increase in clock speed above the 980MHz GPU Boost clock speed in many games with as high as 1097MHz on the GPU core or 100MHz over the default boost clock. This is because the GPU was staying underneath the 100% power target. Still a clock speed of 1231MHz (as high as 1245MHz) is over 300Mhz faster than the base clock speed on the GK104 core and 138MHz higher on the GDDR5 memory (6552MHz QDR). When running through the benchmark suite with the GTX 670 overclocked we saw measurable gains in performance across the board in each game tested.

http://www.overclockersclub.com/reviews/nvidia_gtx670/