GeForce 8800 versus SLI AA and Super AA: performance
Here's how the various single and multi-GPU setups scale across their respective antialiasing modes. I've broken the results out into three separate graphs due to the difficulty of directly comparing the GPUs' various AA modes. All of the graphs have the same scale, though, and we can draw some conclusions based on these performance results and the image quality info from the last page.

There's very little performance hit associated with the CSAA 8X and 16X modes of the GeForce 8800, and given their image quality, I'd say they merit direct comparison to the multi-GPU 8X and 16X modes on the older cards. That gets kind of ugly, though:

The long and the short of it is that the G80's excellent and very efficient coverage sampled AA puts it on top, even without special SLI AA modes in Nvidia's current drivers.