I don't recommend even 2xSLI.
Many games don't support it, and near-future games are even LESS LIKELY to support it as well. WHY?
Modern game engines look for ways to optimize things. One way is to find SIMILARITIES between frames (which is how video COMPRESSION WORKS). This requires the same GPU to work so it does not work with the typical AFR implementation of SLI.
That is why Batman AK could not support AFR. (Alternate Frame Rendering, which most people just call SLI since there's only a couple games that do other methods than AFR such as SFR)
For games that do work there may be added STUTTER/JUDDER or other issues.
I'm NOT saying it's completely crappy, just that I think it's more hassle than it's worth for one thing, and IMO...