ATI's upcoming flagship 825MHz clocked Radeon HD 2950XT can score 528 Gigaflops. These raw Gigaflops numbers indicate that in raw calculations it ends up faster than the original R600 core. At 742MHz an R600 core based Radeon HD 2900XT scores 474Gigaflops which is significantly lower score than what new chip can do.
The key element might be two flops per unit powered 320 Stream processor chip. This is not something new the original R600 managed to do this but still RV670 will be limited with 256 bit memory controller which will have to mean a slower performance at high resolutions.
Still, at a $249 price tag it looks quite good.