Why not, they are voltage locked (NV Kepler) so it's pretty easy to just increase the power percent to the max and increase the core slowly. You could get around 1150-1250 on the core for a decent speed increase. Just find the max stable core in uigine, 3dmark, and then test your games. If the driver crashes drop the clocks a little or if the game crashes or if you see artifacts. Go up in say +20 MHz increments.
The naysayers probably haven't even tried it themselves but the 670 is certainly not powerful enough for max settings in every game so any gain is just a bonus. It's free performance to make your card equal or possibly faster than a stock 680 for less money.