Read this, it's not as simple as 60 fps or 720p is enough.
http://www.100fps.com/how_many_frames_can_humans_see.htm

I personally couldn't stand old CRT monitors at anything under 85hz, but that's noticeable flicker, doesn't mean a 60 fps game doesn't look fluent.
Even 120 fps won't always be enough. The human eye is perfect at tracking moving objects, the higher the resolution and framerate is, the better that object looks while it's moving accross the screen.

Every competitive PC gamer playing goes 60 fps or greater and turns off distracting effects or runs in low detail. What would you rather have, a pretty game where you get stomped on all day or would you rather be winning?

It's not about frame rate you can see but about input lag. Gamer doesn't need 120 FPS in his eyes but that small input lag with it.

4K and 120FPS.

4k is useless and way too much required rendering.

We need to go 1080p vR

Exactly.

Except for life like VR 4K is still too low.
1080p standard is suited for a 30 degree field of view (SMPTE 30), while with VR you want to have at least an 80 degree field of view, or even upto 120 degrees. (Occulus rift uses a 110 degree field of view) So if you want VR at 1080p quality, you need 8K per eye.

You can ease the rendering load if you have reliable pupil tracking, the human eye only sees sharp in a 6 degree field of view, the rest of your 120 degree visual field is peripheral vision which is more sensitive to motion and flicker but has very poor resolution. So if you render in the highest resolution in a 10 degree field of view with 60fps, and render the rest in low resolution with 240fps, you probably get pretty far in tricking the brain that's it's close to real life. (Assuming the pupil tracking doesn't have significant lag...)

Thank you. I read and Ilerned a lot with it.

I was considering  that human eye was like any point-wise analog-digital converter with a aproximatelly 1/30 s refresh rate, so 60 FPS would be enough, according to Nyquist rate. But seems that the eye is much more than this. So, ok, there is no right answear.

But Im still considering that a model could represent well, maybe a full exposure camera. It could explain the perceivment of a 1/500 s blink light, and the (lack of) sensivity to darkness (cos it is quite similar to the afterimage explained in text). It would explain also how motion blur affects the smothness. But it do not explain the different effects in the different areas of the eye..

My lips are sealed, but I can post links all I want.

http://www.playstationlifestyle.net/2013/11/14/playstations-rd-magic-lab-teases-eye-tracking-on-ps4-partners-with-nasa-for-ps4-content/

Motion blur is a neat trick to suggest smoothness, just as depth of field blur can hide lack of detail. The human brain is a remarkable tool for filling in the gaps. Motion blur in real life works quite differently though, as your eyes track objects and in your mind everything stays sharp upto a certain point.
Just spin around in a circle for a while, after screwing up your inner ear (getting dizzy) tracking goes out the window and everything becomes a blur. You're not spinning any faster as before, yet suddenly there is motion blur everywhere.

Anyway a neat trick to suggest fluid motion is to simply turn down the lights and reduce the brightness. In that sense your eyes do have sort of an exposure time like a camera. (next to a chemical process to makes your eyes more sensitive in the dark, comparable to ISO setting) Staring at a bright monitor in a well lit room will make you more susceptible to low frame rates than playing on a dimly lit screen in the dark.
That's one area where games follow human perception, hide lots of stuff in the dark, makes the game look more detailed and seems to perform better than it is. Works in nightclubs too!