RV770 is both impressive and disapointing at the same time.

RV670 Specs:
16 TMUs
320 SP arranged in 4 SIMD arrays of 80sp each
16 ROPs
256Bit DDR3/4 Ram
666Million Transistors on 55nm

RV770 Specs:
32 TMUs
800 SPs arranged in 5 SIMD arrays of 160sp each
16 ROPs
256Bit DDR4/5 Ram
~830Million transistors on 55nm

Now the impressive part is that ATi managed to more than double the number of SPs and double the amount of TMUs and only add about 200Mill transistors. The disapointing part is that overall performance is only expected to be 50% higher than RV670. One would expect more than that especially since RV770 will finally offload AA to the ROPs.

There is no "true next gen" chip for the DX10 generation, even the GT200 is just a revamped G92 with more shaders/ROPs and TMUs. Things in the GPU world will be boring until DX11 comes.