It's typically more difficult to get two GPUs in CrossFire or SLI overclocked aggressively than it would be to run one processor at elevated frequencies. If anything, you're always going to be limited to the peak clock rates of whichever card is slower.
I was surprised, then, to get our Mars 760 card running with a 185 MHz GPU Boost clock rate offset and a 742 MT/s memory data rate boost. Even more impressive, the reported 1257 MHz Boost clock setting was exceeded in both of the apps I experimented with (FurMark and Metro: Last Light), where I saw 1306 MHz under heavy load. Achieving those numbers required the Asus GPU Tweak utility, a 12 mV offset on the GPU, a 105% power target, and a fan speed manually dialed in to 80%.
Now, there is absolutely such a thing as vendors cherry-picking their best GPUs and memory for review samples. It happens all of the time, and we totally get the desire to put a best foot forward. I'm not saying that's what's happening here. But I would also caution our readers to consider our results knowing that we're benchmarking a review sample, and not a retail card. Your mileage may vary.
The result of our overclock is significantly more memory bandwidth than a stock GeForce GTX 690, with comparable shader processing power.
At least in this one application, the overclocked Asus Mars 760 achieves a frame rate that is almost identical to the vastly more expensive GeForce GTX 690. And again, while we obviously can't guarantee that retail boards will overclock as well as our sample, Asus has to be doing some sort of binning to get amenable GK104 processors able to stay under a certain thermal limit anyway. From what we've seen and heard in the real world, the Mars 760 is garnering a good reputation for overclocking well as a result.