no you cannot see a difference between 60, 90 or 300 fps, because your eye can only refresh with 25 Hz - let's say due to no triggered input for your eye, you can distinguish up to 30 Hz.
the thing is: net_graph shows you an average value, so it is not 60 Hz all the time. it can be even down to 20 fps or less for a short period of time. thats what you can see, on average it's still 60 Hz.
So a 60 Hz screen is more then fine, everything else is just imagination and advertisement from screen producers and some ppl really fall for it. Unless you don't use 3D applications, 60 Hz are more then enough. (the screen refresh rate is quite stable - the problem is the pc, so 60 fps are problemetic - because it's an average value)
PS xbox even cuts the upper limit of fps to 60, to obtain a stable value and have lower standard deviation of the fps.