Currently, the GTX680 has wretched Compute performance.
Whether this is due to immature drivers, the lowered SM count, the half speed Shaders or the phase of the moon is unknown.
http://www.anandtech.com/show/5699/nvidia-geforce-gtx-680-review/17
We can just hope that the drivers mature and/or they release the GK110 which will mop the floor with current cards.
I will settle for OSX drivers for GTX680 for now. RIght now it is dead to the world in every iteration of OSX I have tried.