I'm currently using XFX 8800gs which is similar to 9600gso..
My stock clock was 580 core,700 mem,1450 shader - I overclocked it to 700,1000,1850 by using Rivatuner 2.24 with Forceware ver. 182.50 - http://www.techpowerup.com/gpuz/usmc6/
I think I could push it a lil bit more but I'm happy with this already.Some ppl out there even reach more than 730 core!.. you could download it here - http://www.guru3d.com/index.php?page=rivatuner