Nordic Hardware claims the ATI RV770 GPU will be almost 50 percent faster than the RV670:
The upcoming ATI RV770 is not meant to compete with GeForce 9 series though, but with the true next generation, G100/GT200.
At the moment, Radeon HD 3870 and GeForce 8800GT is pretty much on par, with a slight advantage for the latter. But when the GeForce 9 series arrives, the only card that will be able to compete is Radeon HD 3870X2, which on the other hand does it well. With the coming launch of CrossFireX, ATI will still be able to compete with NVIDIA, just not in single card configuration (3870X2 aside).
The current state of RV770 of indicates that it should perform up to 50% better than RV670, which is pretty much what we're expecting (since this is the kind of leap you see with every generation...). The best thing about this is that ATI is on schedule for once and we should see the card in June, expect leaked benchmarks in May.
The thing is that RV770 is "only" 50% faster than RV670. G92 is faster than RV670. If GT200 is 50% faster than G92, ATI will still have to rely on CrossFire to remain on top. On the other hand, ATI has been wanting to move the focus from raw power to multi-core for some time, and if CrossFireX scales just as well with RV770, there's no reason to be alarmed. ATI just have to convince the buyers that single card is out, multi-card is in.