I usually set everything up in any game to hold 75 FPS or so, which isn't too difficult as I built this system a couple of months ago.
Here though, I'm holding from 40-75 or so, when it's low it's likely there is smoke on my screen. Doesn't seem to matter, going from High+Ultra combo mix to full on low I still only got 80 FPS consistently.... 40 is about my threshold now, before I had ye olde coal fired PC, and 30 was my number. Can't bear that anymore.
I set up things as such though to have some buffer zone. I can easily tell the difference between 30, 60 and 90+. And yes, there is a difference. You may not even see above 60 due to the eye / monitor, but the controls just feel different.