FUD Zilla claims ATI's RV770 GPU will be 1.5 to 1.6 times faster than the current RV670:
In the real world, this should mean that if one game gives 50FPS with RV670 that the new chip should be able to get you around 75FPS at the same settings. On average, the new chip will have to be at least 30 percent faster than the old one to make you even consider it, but at least specification-wise there is not anything that you might miss.
RV670 was a shrunk and a better speced version of R600 with 512bit memory controller crippled to 256-bit; and it looks that R770 will get that memory upped to 512-bit again. At least we know it will end up being fast, but we still don’t know what Nvidia’s real answer is to this one.