NOWHERE near i'm afraid.
Dual Card solutions are ONLY worth it if you run a REDICULOUS resolution, if you have THE top of the line cards (2900XT's / 8800 Ultra/GTX) or if you get the REDICULOUSLY cheap.
SLi is buggy, unreliable and tbh a bit naff for the cash you spend, and the only rewards tend to be more noise and power consumption. Same for Crossfire, although the gains tend to be a little more "average" (SLi can, in some extreme cases HURT performance thanks to the extra CPU load!)