The impressive thing at first glance is just how close the performance of the GTX 690 and GTX 680 SLI is. Despite having a much lower base clock the GPU boost tech manages to get the twin GPUs up around the same sort of performance.
The next thing to note then is just how close a pair of GTX 670s gets to that performance.
At this level the sort of performance drop you're getting between the two options would be very difficult to see in-game.
DirectX 11 tessellation performance
DirectX 11 gaming performance
DirectX 10 gaming performance