Seems SLI still polarizes a lot of people (and considering there's a prevalence of AMD users, there's usually a lot of back-and-forward banter on the forums).
I consider myself to be a pragmatist PC gamer. Last year I got a second GTX 960 4GB to SLI with my first one, knowing full well there were issues, but at the same time going out on a limb just to try the technology out. It was an economical choice. I got the second GTX for £110, which gave me performance (in SLI games) similar to a GTX 1060 6GB. Which was what I wanted.
Games I tested it with: The Division, Fallout 4, SW Battlefront, Mass Effect: Andromeda, Battlefield 3 & 4, GTA V, Warhammer Total War & Rise of the Tomb Raider. I also tried to get a few non-SLI titles to work, but results were, at best, horrid.
In general, performance in SLI-enabled games was great. Really really great. Smooth as silk and framerate up the wazoo (in an old rig gaming @1920x1080). I had no issues related to performance. No stuttering, nothing. However, the Nvidia software did require tweaking settings in the games I didn't want SLI to try and do its thing.
Later, I uninstalled card #2 and stuck with just the one. Why? I actually just play one game for extended periods of time, and SLI isn't really doing anything for it (Unity Engine, based, say the developers). I even thought about recording gameplay and tried to get shadowplay to run off the second card, but it always defaults to the one rendering the game. (if anyone knows a workaround, tell me). So there's no real point to having both cards installed.
I'm about to sell both my GTX 960 4GB and the SLI bridge and switch to a single 1060. I pay a little more upfront, sure, but it's a single card, which doesn't steal that much space in my case, draws less power and performs slightly better in all games (rather than just a few choice SLI titles).
I think the 1000-series GTX cards broke the SLI rationale. In the old days you'd have, say, a GTX 460, and when the 560 came out, you'd have some 20%-ish gains. You could buy the new card, or, get a good deal on a second GTX 460 card and set up an SLI rig. With the transition from GTX 900-series to GTX 1000-series, two GTX 960s (4GB!) come in at roughly the same performance as the GTX 1060 (6GB). There's no longer any reason to buy into the tech, and even less if you factor in the lack of AAA titles and the reported bugginess some people claim to experience.
