You got a nice overclock on that 9600GT. Mine won't play nicely in Crysis until I drop to 750MHz. Unfortunately ATITool can't detect artifacts no matter how much they fill the window with yellow, but just looking for them myself I didn't see any at 770MHz. Crysis just caused driver crashes all the time, which fortunately recovered every time. I only have my memory at 936MHz, I don't know how high I can go with that, but probably not far. The same crashes occur with the shader clock above 1770MHz. This was done via rivatuner with 174.74 drivers.
Just to let you know, the coders of NiBiTor are working on fan control, but they don't have enough 9 series BIOSs (especially 9600GT).