OCC has published a review on the Sapphire Radeon HD 5970 OC

Overall, I was able to run the card higher than the clock speeds on the HD 5870 for a nice increase in performance, but to do so brought out the fan noise that ATI reference cards always bring to the table when you bump up the fan for additional cooling. I was able to reach clock speeds of 890MHz on the core and 1260MHz on the memory, with power consumption peaking at 486 watts on the system under load with temperatures that reached 69 degrees Celsius. The vapor chamber cooling does its job keeping this behemoth cool! Not too bad on the clocks and temperatures, but as an enthusiast you always want more performance with less power.

Sapphire Radeon HD 5970 OC Review