Didn't knew that, got to be bottering
But as you say, I have heared that human eye can "see" and react on 30 FPS. But then some people means it higher, lower etc, and in the end it might varry a lot from person to person.
And, it's a matter of adapting. When I play AOC, like I have done the last month I usually has like crappy FPS below 30, but still seems smoth on like 15-20 FPS, and excelent at 30 FPS. In LFS when I play that I need to have 40-50FPS before I feel it goes "smoth", ofc the speed of the gameplay is faster in LFS, but I'm talking not about slowdown effect, more like a sirup effect that makes it sluggish and slow.
Maybe it varry's from game to game, I don't know, but I know that different people will have differnet point of veiw on what's "smooth" FPS.
Maybe it's based on your reaction or something, who knows?