The Guru of 3D takes a look at NVIDIA 3-way SLI
A quote from the article:
NVIDIA 3-way SLI review - 8800 Ultra
If you had a close look at the 8800 GTX & Ultra, you'd notice there's a second SLI finger (connector) and to date there has been a lot of speculation about that extra connector, to name one .. it could have been an extension for physics over a third card. The truth is often to be found in the most simple and logical solution, it was all about SLI from the get go.
If you have one of these rather expensive cards you can now link up three cards and enable 3-way SLI. Guru3D takes three XFX GeForce 8800 ultra's for a quick test-drive, you could call it a three-some.
NVIDIA 3-way SLI review - 8800 Ultra