FUD Zilla claims the RV670XT will have a raw calculating power of 528 Gigaflops - which is more than the current Radeon HD 2900 series.
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.
It's expected that the Radeon HD 2950 XT will cost around $249.