Briefly tried Vantage at the extreme preset with 10.3a. I got 10347GPU.
Card was @ 1050|1300 with the fan pegged on blow dry.
That's a single HD 5870 @ 1050|1300 with the fan pegged on blow dry. I'm probably going to drop a waterblock on this card because those clocks are not problematic. I've seen guys at XS going all the way up to 1100 on the core with water cooling. Of course that's rare. I've been up to 1070 briefly with the stock cooler and it freezes after a bit. I should note that's with MSI's Afterburner and appropriate voltage boosts.