I was thinking my first slot is a 16x bandwidth then next is a 4xmode then 16x then last 4xmode. Should I just go for a regular crossfire with two bandwidth 16x's or should I go 3way crossfire? And can I skip a slot to get to a 16x or does it have to be in order 16x,4xmode,16x,4xmode bandwidth though!!! I was just thinking to just skip the 4xmode and just hit the 16x?, is it worth doing a 3gpus crossfire or just two gpus crossfiring? My mobo is M5A99FX pro r2.0 I have four PCI slots at 16x just 2 run at 4x mode, the 3 or two graphic cards I want use it for is a amd 7970
Your MB manual will verify the layout of the slots. And it will also tell you which slot needs to be populated first for best performance. I would stay with 2 way SLI in the 2 PCIe X16 slots. The only slot that would be practical for a 3rd card would be the one closest to the bottom of the MB. But that presents problems with accessing the FP headers because it will be covering them.
However, if you are gaming across 3 monitors (5760x1080), the 3rd card will help with performance.