We were only able to achieve a stable core clock of 670MHz per GPU with the GDDR5 memory clocked at 1800MHz (3600MHz DDR). This is a far cry from the GTX 580's 772MHz core speed and 4008MHz DDR frequency.
This 10% overclock did provide 10% more performance when testing with Crysis Warhead. Sadly, we only received a 3% performance boost in Just Cause 2 and 6% in Aliens vs. Predator and Metro 2033.