Expreview compiled a handy table which explains the changes NVIDIA made to its GeForce 9600 GSO. This card was originally a GeForce 8800 GS, after some small changes it became a GeForce 9600 GSO this year and now NVIDIA plans to give the card another core:
New version of GeForce9600GSO is based on G94 core, and the amount of shader reduces to 48 (9600GT has 64SP), but memory interface keeps at 256bit, memory size will be 256MB or 512MB. So we can take it as a shrinked 9600GT. It is sure that the new 9600GSO will have lower performance than G92-9600GSO and 9600GT, but hopefully it can bring its price down.
The card will be available by the end of this month and it will try to compete against the ATI Radeon HD 4650.