The guys at the Inq have come across something funky on their test bench. It seems that when you put two 8800 Ultra cards together in SLi, the drivers will drop the core & memory speeds down to near-GTX levels. Not only that, 3DMark06 wouldn't run. Interesting...

"Two identical 8800 Ultra cards, both working fine on their own at overclocked 645 / 1120 speed, can't get together even at the default setting. Again, the drivers were the newest, the platform one of the best boards around, and no penny pinching on any of the components..."