oops. mis-read that. either way you dont' really notice a difference between 30FPS and 60FPS. saying 30FPS isn't smooth is the same as saying 60FPS isn't smooth. if it doesn't appear smooth it's either 1) not displaying at 30FPS and you're getting lag in your rendering 2)you're on the far end of the visual spectrum and capable of viewing things at greater than 30FPS
I've seen movies in 60FPS. i've seen the same movie, on the same projector at 30FPS and not noticed a difference. 60FPS projectors typically have better color capabilities and far higher resolution. this improves quality FAR more than FPS. Also keep in mind these movies are recorded at 25-30 FPS. displaying them at 60FPS doesn't improve anything, you're just seeing more 'blur'. but what really sets it apart is the resolution. not the FPS.
a lot of people tend to forget that for some reason. it's not the FPS you're noticing. it's the improved resolution/color display. a dirty little secret: a lot of TV/projector companies will tell you FPS is important so they can jack up the price. you should really be looking at resolution more than FPS.
If you go to Tiger Direct and look at TVs on sale, you may see a 42"1080i that's cheaper than a 38" 720p. most people would think 'Hey! what a deal!' but the 1080i is 1680x1050 resolution 10000:1 and the 720p is 1920x1080 20000:1. I personally will go for the 720p for the higher resolution and contrast.
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EDIT:
you updated your post so i will too.
eyes do work in energy. at 1000FPS, a single frame is displayed for 1ms. you will see it, but you won't really know what you saw.
the human eye can differentiate up to 15 images per second. most people are below this. this doesnt' mean we are caped at 15 FPS. it's just anything above that our brain won't process. it's too much information.
so yes, technically speaking the eye is capable of seeing more than that. but the brain can't keep up. it's like playing sounds above/below the spectrum our brain can process. our ears pick it up, but it's junk data to our brain so it just throws it out