We today decided to use the Xtreme Tuner HD software again. We were impressed with it when we overclocked the Galaxy GTX 470 by itself and since we found out it supported SLI overclocking, we thought we were onto a real winner.
Due to the fact we're running SLI, we didn't want to be as aggressive with the overclock as we did before. In saying that, though, we set both fans to 100% to make sure the clocks we got ran as stable as possible.
What we ended up with was a 775MHz core clock, 1550MHz Shader clock and a 3820MHz QDR memory clock. While it's not quite the 803MHz / 3932MHz QDR clock we offered in our stand alone overclocking article on the Galaxy card, it's not that far off. Considering we're starting at a core speed of just over 600MHz, this really is a massive overclock for two cards. Before we go onward, I'll mention that the setup was 100% stable at these speeds.