I recently dumped my 120hz monitor since i was able to overclock my cheap Asus monitors I use for eyefinity to 76hz using ToastyX. EVGA also has a tool that can be used with Gefroce GPUs. 

The 120 hz monitor still has an advantage in terms of input lag (120 inputs per second vs 76) but visually I really can't spot the difference. They say human eye can't see the difference after 60 hz/frames per second...Well I can confirm that I can't see a diference between 76 frames per second and 120 frames per second. None what so ever.

If someone decides to do this though, be warned that you may experience blue screens and eventually even have to reformat your PC if you screw up some some of the monitor timings/settings and resolutions. Have a backup handy and you have nothing to worry about. 

Yeah there is a difference between 60 and 120 for sure...but most of that difference happens at 70-80hz. After 80 you'd really be straining your eyesight to see any difference. I was shaking my minimized windows back and forth between both monitors and doing all these tests and I can't see any visual difference. 76hz that my monitors achieved is about a 22% increase of frames per second over 60 and the cool thing is that when you set that as the default, the VSYNC automatically becomes that. So all games start running at 76 fps if your GPUs can push it, which for me in eyefnity is a lot more achievable than 120 fps on 3X 120hz monitors.

Tells you that those 144 hz monitors Asus is selling are kind of a scam. 

nope

I overclocked mine from 60 to 66, because anything after 66 the screen just goes black and goes back to normal. I can say for sure though that it does seem a tiny bit smoother since it can show 66fps now instead of just 60. I used the EVGA overclocking tool, really simple to use.

Good stuff. Yeah I saw plenty of black screen after 76hz.

I found is that if I lower my res to something like 1600x900 I can push as high as 80hz but at 1080p 76hz was max. 

Yeah there is an input feel diference for sure. When you push left on a controller at 120hz, the input lag you can experience is 1/120 second while 60 hz has 1/60 second.

There are other problems too which make input lag more apparent regardless of refresh rate. For example, monitor it self has input lag on top of refresh rate.

If we take the XL2420T 3D 120 hz monitor as an example below(monitor I had), it has input lag of 13ms. So the maximum input lag it can have running at 120hz is 13ms + ((1 /120) *1000) =  21 ms

Dell S2740L for example only has 3.2 ms input lag so it actually has less lag than the 120hz BenQ. (3.2 +(1/60)*1000) = 19.8