Got Me Three

TRI SLI is what I am talking about. Bought the third card for me rig,

Nice.  

yup, Tomb Raider is definitely one game that highlights tri-sli!  good drivers (look at how horrible Witcher 3 handles it with actual negative scaling) do wonders.  NvLink can't get here soon enough to unleash the real power of multi-gpu configs.    

I hear a lot of negative comments about tri-SLI. It's definitely not for everyone, and if you're running at 2560 x 1440 then it's overkill. It's also an expensive option, because you frequently need a bigger case and extra cooling.

However, I've been running tri-SLI since 2008, and I absolutely love it. I wouldn't have it any other way. It's nice knowing that my machine is running as fast as possible for the vast majority of games.

Here is a good summary of how current games scale with 2x vs 3x SLI:
     http://www.guru3d.com/articles_pages/geforce_gtx_980_sli_review,1.html

And here is another:
     http://www.maximumpc.com/geforce-gtx-980-ti-3-way-sli-overkilling-it/

In that first article, 75% of the games scale reasonably well. The others don't scale, or they scale backwards a tiny bit. (The backwards scaling is so small that it's basically identical to 2x SLI.)

Is 3x SLI overkill? I think it is if you're running at 2560 x 1440. However, if you're running at 3840 x 1440 or 4K then it definitely becomes useful. My goal is to run all games at 3840 x 1440, quality settings at maximum, and maintain 100 FPS in all the games that I play. That generally requires 3x SLI.

Do I really NEED it? No. I could easily lower the quality settings a tad, or be happy with 70 FPS on many games. But here is my thinking: I went to the trouble of getting an exotic liquid-cooled machine to play games without compromise. Then I got an amazing ultra-wide display with a 100 Hz refresh rate...once again to play games without compromise. After all that, and after spending $5000+ on equipment, should I hold back and skip the 3rd video card? No way!

So if you have a big case, excellent cooling, a compatible motherboard, and you game at resolutions higher than 2560 x 1440, then I think it's worth the extra bucks to by the 3rd card.

Yeah...I see what you're saying. The comments regarding 3x SLI aren't usually negative. They are just setting expectations. It's important to know that you won't get 300% better performance with 3 cards.

I remember considering 4x SLI back in the day. That's definitely beyond my pain threshold: Too much money for very few performance gains.

I never heard about NvLink until you mentioned it. Ouuuu...now that sounds promising!