Asus P9X79 Motherboard Review

The Ninjalane Multi-GPU index is a portable set of data we can use to determine the multi-gpu potential of any motherboard.  A higher index number indicates a favorable condition for multiple graphics cards while a lower number indicates a hindrance in one of our leading indicators.  Since the Index is not dependent on system architecture it can be applied to any motherboard regardless of processor or chipset generations.

Index: 6.5
Optimized: 2x
Max Support: 3x

NVidia SLI
AMD Crossfire

This motherboard will support up to three graphics cards and is optimized for dual card operation.  For best video performance you will want to populate slots 2 and 5 and enjoy the triple slot spacing or use the Asus cards with triple slot coolers.
 
The board will run in three-way CrossFire configurations however given the location of slot 7 it is likely intended for expansion cards or dedicated PhysX processing.  You will also have to contend with limited space given that this is the last slot on the motherboard.