i currently have an 8800gts superclocked 640mb that i can stepup to the superclocked gtx but for a bit more i could simply add a second gts which is my best option?
I think the 8800GTX would be the better idea. SLI still isn't completely dependable. Some games it may give little to no extra performance over a single 8800GTS.
With my 8800GTX, I'll have more dependable and consistent expectations.