When it comes to the point of “Enthusiast Key” which generally indicates of not supporting more than two cards in SLI,Nvidia has changed their stance where they will unlock 3 & 4-way SLIs.
The enthusiast key will be no longer required and and future drivers would support it as well which however will only work with selected applications, games and synthetic benchmarks.
We still recommend not to buy more than two units as the programs are selective and you probably couldn’t use all the required apps and games you longed for.
According to Nvidia’s statement on this point:
“With the GeForce 10-series we’re investing heavily in 2-way SLI with our new High Bandwidth bridge (which doubles the SLI bandwidth for faster, smoother gaming at ultra-high resolutions and refresh rates) and NVIDIA Game Ready Driver SLI profiles. To ensure the best possible gaming experience on our GeForce 10-series GPUs, we’re focusing our efforts on 2-way SLI only and will continue to include 2-way SLI profiles in our Game Ready Drivers.