The 9600GSO is just a "crippled" 8800GT. The 9600GT is based on a slightly different chip (G94), has a bigger frame buffer (512MB vs. 384MB typical), and has a higher memory bandwidth thanks to it's 256-bit interface, as opposed to a 192- or 128-bit memory interface of the 9600GSO. Oh and in some cases the GSO is a renamed 8800GS as well. In benchmarks I've seen, the Radeon HD3850 256MB is faster than an 8800GS/9600GSO, and the 9600GT is certainly faster than an HD3850, so the 9600GT is faster than a 9600GSO despite having fewer shaders.