The more I hear about Cayman, the more I doubt ATI's ability to beat the 580 performance wise. I know that core design and optimisations are very important, and that ATI are current ahead in this area, but can they really overcome a ~30% transistor deficit and ~20% memory bandwidth deficit?
My opinion is that the 6970 will only match or slightly exceed the GTX580 if the cores are pushed very close to their limits. 875-900MHz seems the probable default clock range and overclocking is unlikely to yield more than 1000MHz on a core which is larger than 5800. This leaves NVidia room to release an Ultra version of the 580 with clocks north of 850core. All 580's seem to reach 900MHz+ on stock coolers with a little voltage bump.
So there you go, +1 person for 6900 being ultimately slower than GTX5x0.
My opinion is that the 6970 will only match or slightly exceed the GTX580 if the cores are pushed very close to their limits. 875-900MHz seems the probable default clock range and overclocking is unlikely to yield more than 1000MHz on a core which is larger than 5800. This leaves NVidia room to release an Ultra version of the 580 with clocks north of 850core. All 580's seem to reach 900MHz+ on stock coolers with a little voltage bump.
So there you go, +1 person for 6900 being ultimately slower than GTX5x0.