If you were going for a god system with Sandy Bridge-E and QUAD 580s, would a fourth GFX lower performance? I read on Google and such that QUAD SLI would actually lower performance relative to a TRI SLI set up. Lets say if you had a mobo that supported x16 all across, would that still lower performance? Or is that the problem, no mobo supports x16 all across? Is it driver problems?
The problem is not bandwidth , it's purely a driver support issue.
This affects both ATI and Nvidia in they're Quad setups. A lot of games don't have profiles or cannot support quad gpu's resulting in Negative Scaling (less performance then say 2/3 cards while using 4 gpus)
In benchmarks Quad performs really well, in real world gaming it can be a pain in the ass with constant problems and performance loss, and driver fixes seem to take a lot time for fixes related to quad gpu as opposed to 2/3 gpu which tend to get fixed much faster.
Having had a Quad setup for a couple of years now my next upgrade I will be going Triple GPU's , getting awesome benchmark scores is useless if you can't play half the games properly.
No, there is no point of Quad SLI/Crossfire in my opinion, because the drivers are not supporting the setup. If you already have a Tri-SLI/Crossfire, I recommend you to stop and stick/stay with your configuration until you decide to change your Graphic Card configuration and not to add any more card to make it Quad SLI/Crossfire, because that will waste your money .