@Benjamin: As i write, people I know have tested or bought such screen and saw inn front of their eyes what it is.
@mmnicolas: maybe it is only to steal our money.... or not. I remember this 800*600 screen... I'll never go back under full HD now.. I'm sure these 4K screen in a decade will be normal things to have and I'll never return to fullHD because I'll be used to have pixels I can not see on screen because screen has so high definition.. (by the way I don't know 17" screen for 4K, for me it is for big screens, TV screens)
So you guys tested the difference between 30/60/120 in real life? To be sure of what you say, you have to, that's why I trust the people I know who tested it. Now I don't think anymore there is no difference, because my friends tested and told me there is a huge difference in what you see/feel on the screen.
If you guys know there is no difference because.. you know it, it is sure, because you say it, this is not really trustable, you don't even see it with your eyes and you have certitude..