No amount of extra hardware is going to make a game feel smoother. If you understood how games 100% were made, how much coding is involved, how drivers work... You'd realise that what you're looking at is a number, and regardless of what that number is, be it 60fps or 600fps, the fact still remains, your CPU will bottleneck the cards, there may be microstutter, the part of the game that gives you lower than 60fps, is part of the game that may not be coded so well.... It's not your hardware! It's all 100% software, you can make games look stunning on old hardware, it's how the coding is done.
But since technology keeps moving so fast, do you have any idea what programmers have to do? Every few months something new is out, so every few months everything has to be updated, corrected, fixed.... you can't account for it, neither can your hardware. You'll definitely hit 60fps+ but you won't feel it, there's different types of lag you have to consider. Such as, input lag, monitor lag, heck, even you blinking is lag. You can't throw money at these issues for them to go away. They never will. Tweak the settings, spend less money, and be happy with a single GPU, no microstutter, and SMOOTHER, yes, smoother, gameplay. Single card + lower settings = smoother gameplay.
I'm not going to continue telling you what everyone who knows anything about games knows. But you definitely should consider a single GPU setup for a smoother performance. I have a friend who works for intel, making drivers for CPU's etc... he goes through more components you can shake your money at just getting the damn drivers to work.
I hope this is clear enough for you, I'm pretty sure you'll still go with multi-GPU's, but honestly, after researching, finding out how everything works, you'll probably agree with me.
No one can argue with the facts, however, SLI/crossfire, do perform faster, but not smoother. Either way, it's probably that minute you couldn't tell anyway, same with lowering settings to enable higher AA. But even then, you don't need AA at 1080p resolution.
Hope this helps, and whatever you choose, you'll be happy. And the FPS scales with your refresh rate, it can't display any higher than your refresh rate.