According to a report by Fudzilla, ATI's upcoming DirectX 11 GPU - known as RV870 or Evergreen - is roughly 1.6x faster than the current RV770 chip. RV770 powers ATI's Radeon 4870 graphics card, which is among the top performing single-GPU cards on the market. I suspect that a performance leap of 1.6x is mostly in theory - or in an absolute best-case scenario. Regardless, ATI's approaching 40nm offering should be an impressive step forward in the never-ceasing GPU arms race.
Meanwhile, the Nvidia camp is prepping their November response to ATI's Evergreen line. Nvidia is working on a GT300 card, which supposedly features 512 processor cores among other architectural enhancements including MIMD (Multiple Instruction Multiple Data), an improvement over the presently utilized SIMD technology.
It is alleged that Nvidia's project may outdo ATI's in terms of performance, but at the expense of a larger, hotter card.