VR Zone got their hands on a 3-way SLI config with a 790i SLI based motherboard, three GeForce 8800 Ultra cards and a Core 2 Duo E6750.
Here's a little writeup of the results:
Using the Forceware 167.10 3-way SLI beta drivers on Windows Vista, we need to tune up the AA/AF to actually see the performance differences between 2-way and 3-way SLI. We got a 26% improvement in 3DMark06 at 1920x1440 resolution, 8 sample AA with 16x AA Quality and 16x AF over 2-way SLI. Without AA/AF, we got only a 5.6% performance boost. Nvidia is still working hard to enhance the 3-way SLI drivers further so we hope to see a bigger FPS boost in latest games which are more GPU intensive with better multi-GPU support. So make sure you run those intensive games to high resolutions like 1920x1440 or 2560x1600 etc with all the image quality settings to the max to enjoy full benefits of a 3-way SLI setup.