I first went SLI with the 780Ti and never looked back, had the 980's in SLI and now the 980Ti's.
SLI performance in the main games that I play like GTA Online, The Crew and the Division are extremely good. SLI scaling in these three games is pretty much perfect, I can get 99% usage on both cards easily if a particular area is demanding.
It is a pain when some games don't support SLI so you are forced to use one card. Batman Arkham Knight was supposed to support SLI but the developer did a crap job and it never worked as it should have, that game now only uses one card unfortunately.
I personally don't see any micro stuttering but this may vary from person to person. I am quite fussy with image tearing and stuttering and I find the frame rate very smooth when everything works ok.
I personally could never go back to a single card as I really like the extra performance SLI is capable of providing as long as the developer does a good job. No idea what things are going to be like when DX12 goes mainstream but DX12 should be amazing for multiple GPU's as long as the developers do a good job supporting it.
I tend to game at 3325x1871 or sometimes 4K or even 1440p (using DSR) if the game is really demanding in SLI with all settings maxed out (no AA) to maintain 60fps. The image is downscaled to 1080p for me and games look really sharp and crisp.
I know, two 980Ti's and a 1080p screen but even two aren't quite enough on occasion for what I do with them