well from what I have been told is that sli isn't really needed till at least 1920x1200 resolution so in that case I would go with the 8800gts 512 mb (g92) single card,but if you are **** bent on going sli I've heard the 9600gt's in sli scale upwards to about 90% and get awesome gains in sli. cant say this first hand but everyone seems to agree
only if you are only using 1600x1200 resolution though