The quick and dirty:
The Quadro is geared to the CAD Workstation market and isn't optimized for gaming. The GTX 680 is geared more to the general use and gaming market and doesn't perform quite as well in the CAD realm.
If you want to go with the GTX 680, which is better for gaming, I would get the GTX 770. It is slightly faster than the 680, a more updated version with more likely longer support life, and costs a lot less even though it is better. If gaming is not your priority, then the Quadro 4000 is something to consider, but for gaming, the GTX 770 is me recommendation.