Word is going around that NVIDIA is planning to introduce an updated version of the GeForce GTX 260 by mid-September. It's unsure whether this version will be made on a 55nm process but according to Expreview the new chip will have 24 more shaders. This should make the card more competitive against ATI's current offerings.
The original GTX 260 have 8 TPCs (Texture Processing Cluster) totally, but the new GTX 260 have 9 TPCs. That means the numbers of shader processor have been increased from 192 to 216. In G200 chip, one TPC contains 24 shader processors.
Other than the TPC upgrade, the other specs are keeps the same. That means the card still runs at 576/1242/999Mhz (core/shader/memory), Memory interface keeps 448bit, and memory size is 896MB.