Eh, try this test then:
Look at a picture in the picture viewing app on your monitor at 1:1 resolution. Then, drag the picture left and right. Alternately, look at a web page with smooth scrolling turned on and.. scroll.. it.
If your monitor is 60hz or less, you will almost certainly be able to notice the issue. I submit that 120hz is not enough make moving a static picture around look like you're simply moving a static picture around.