We've learned that Nvidia is working hard to launch GT200 55nm, but this will most certainly won't happen in August or September. Our sources imply that this will take place in Q4 2008.
Nvidia simply wants to win the performance crown back from R700. Adding GDDR5 memory and 55nm process will certainly speed things up and they will take the dissipation down.
Thermal dissipation is Nvidia's biggest problem, as the chip turns to be extremely hot and the new 55nm should be a bit better. Once you take care of thermals, you can clock the chip higher which eventually means more performance.
The 55nm process with a new clock and GDDR5 memory should get GT200 55nm a bit faster than R700 and this is exactly what Nvidia needs.