PharaohAmir :
I suggest you to get a dual GTX 970 G1 Gaming setup, since my GTX 980 G1 Gaming runs CS:GO at 4K maxxed out at somewhat 150 FPS.
You don't actually get 150FPS though. The monitor updates the entire screen at 60Hz.
It's a bit more complicated than this because monitors don't update the entire screen at once (otherwise going beyond 60FPS would give no benefit at all). Let's say your GPU creates 300FPS (5X more than the 60Hz can draw). To oversimplify, you basically get 20% of the screen updated per frame. So yes, you get more info to the screen quicker but only part of the screen.
(as an aside, it's also why some games don't appear smooth despite showing a constant 60FPS for example. Programs like FRAPS can report partial frames as a full frame so the "60FPS" might only have 20 full frames and 40 partials)
You're also going to get screen tearing due to these mixed pieces of course, since you've got 5 or 6 different pieces (at 300FPS on 60Hz monitor) from consecutive frame output.
On the other hand, at 144Hz using GSYNC you can have up to 144FPS without screen tear while also having no added VSYNC buffer latency, and if you want to use VSYNC OFF for some reason it's still better than running on a 60Hz monitor.
4K is just not optimal for gaming due to the low refresh rate, and the visual difference in a game like CS GO is incredibly small especially considering the MUCH, MUCH higher graphics demand.
4K often gives only HALF the frame rate (varies quite a bit though), thus requiring more than DOUBLE the processing power since SLI/Crossfire never scales perfectly. Thus, at 2560x1440 a single GTX970 will give a higher frame rate than 2x970's at 4K. It's just not worth it IMO.