We have seen some marketing talk from the DAAMIT machine and it was funny to read that its upcoming RV770 mainstream chip will end up twice as fast as RV670.
Well this is probably right but this would naturally be the best case scenario. You should count on average 20 to 30 percent performance improvement but in some resolution and at some settings, the new RV770 might really leave the RV670 aka Radeon 38x0 cards in the dust and score twice as fast.
It is possible as we could see with 9600GT that ends up twice faster than 8600GT but mainly because of the 128 versus 256bit memory controller and the fact that the 8600GT was barely faster than the old 7600GT to begin with. "