50 Hertz (cycles-per-second) is about the upper limit of recognition due to a phenomena known as "visual persistence". Of course, that is an average only...some stop seeing flickers before that, some can still see a flicker above it. Visual persistence is the reason that the electric company transmits power at a certain frequency...people don't see flickering in their lights.
You can experiment with where your own limit is by changing your desktop refresh rate until you see a flicker or the image seems to be somehow "awkward"...it may seem slightly out-of-focus or it may seem to be slightly less than solid, the effect is different for everybody. If you actually see flickers you've gone too low.

Remember the refresh rate just before the effect occurs and then set your desktop back to it's original value. The value you found that is just above your point of recognition you can now use as your maximum frame rate...any increase in framerates above that can't be seen by you...so why have the hardware work to acheive them?