When a PC renders an image for display, that image is a complete, high-quality snapshot of one instant in time, like those little yellow-pad flipbooks we all used to make in grade school. There's no motion blur (1, although it is technically possible, and 2, Oni's cool blur effect
doesn't count) to fool the eye into seeing more "intermediate frames". As you can imagine, insert more frames into the same amount of time, and you have literal intermediate frames, giving a smoother image.
I refuse to believe that there's a "reasonable" limit to what the human eye can see. Our rough estimates are only based on what we've experienced, so saying "200 fps is a limit" is completely unfounded imo. Until you reach a point where frames are flashing by faster than the light can travel to your eyes, or more reasonably, faster than the electrical impulses can reach your brain, then let's talk about limits. However, I think that a person accustomed to watching a 500fps screen is going to notice right away when that drops down to 250fps.
What that means is that everything helps. It's so much easier to shaft-someone mid-air far range rail-shot with SLI, and that's the straight truth. While the absolute "minimum" acceptable FPS is a matter of personal tolerance, you're not going to realize your full potential until you're able to pull of shots and stunts at the limit of your natural reflex. This concerns both the speed of your fingers and the speed which you can take in signals from the monitor and process them in your mind. For me (and this is a pretty subjective test), it's between 80fps and 150fps - the point where it became easy (or even possible) to consistently hit and hold a shot on someone in midair. Anything above 150 didn't make too much of a difference either way.