Simple test: take some benchmark thats running at @120 FPS. Hook it up to both a 60Hz screen and a 120Hz (native; none of this "Truemotion" junk Samsung/Sony push on TV's) screen. Do a blind test on which is smoother.
The human eye can *distinguish* a heck of a lot more frames then it can pick out individually. In other words: While the eye can't pick out individual frames much beyond 30 or so, it can distinguish the difference in motion between 30, 60, and 120 without issue.