First time I ever went SLI was with the 460 Ti's.
I vowed to never go SLI again.
After NVIDIA screwed me with the 780 Ti's release, I went SLI to extend the lifespan of my system until Pascal's release. Bought a used 780 for $200, ontop of the $700 I spent for my REGULAR 780 many months after release. There was zero mention of a "Ti" card coming out, let alone one of their highest end card (sans titan).
After running SLI again, it made me never want to run SLI again.. again. Reminded me of all horrible issues with it, from poor scaling, microstutter and insane heat output (top card is literally 15C higher than the bottom).
Not to mention multiple GAME ENGINES (UE4) have no support for SLI, and the games that actually work with SLI all have either poor scaling, or multiple rendering issues. I can't recall the last thing that came out in the past few years with great SLI support that wasn't a benchmark utility.
There's a lot more to a gaming experience than "FPS", and almost nobody (tech sites) looks at them. It's an atrocity.
The only objective benefit to a multi-GPU setup is being able to run applications on individual GPUs based on what monitor they're on. This makes multi-boxing a much better experience... unless you're using anything but Windows 10 with WDDM 2.0, which finally fixed the atrocious multi-monitor issues plaguing Windows since Vista.
Wish we could go back to the days of Windows XP..