4K monitors are great, but some devices will output only 30Hz by default, which is awful. I was able to configure my Macbook Pro to run my Samsung U28D590D 4K monitor at native resolution and 51.7Hz, while apple only says 13.3" Macbook Pro supports only 4K at 30Hz via HDMI or Thunderbolt - DisplayPort.
Improvements are so much better. Mouse cursor moves smoother, 60 fps video looks better, document scrolling is smoother, in general 52Hz is definitely usable refresh rate, while 30Hz is very bad. Huge workspace is great, but 30Hz is huge downside to it.
Lets start with things we gonna need:
This wont work over HDMI, so if you was using HDMI before, get rid of it and get Thunderbolt to DisplayPort cable, mini DisplayPort to DisplayPort 1.2 cable also will work. We also gonna need SwitchResX app. It costs 14€, but you can use it 10 days in trial mode.
Install SwitchResX Preference pane and open it. On left side you will see your monitor model, click on it, and on navigate to "Custom resolutions".
Press "+" to create new resolution and fill form with these settings:
Press "OK" and close Preference pane, it will ask you if you want to save changes, confirm this.
Open SwitchResX preference pane again and navigate to your monitors Custom Resolutions again. You will see that your newly created resolution status is "Reboot needed". Reboot computer.
After reboot open SwitchResX Preferences pane again and this time open your monitors "Current resolutions". Your Custom created resolution will be there, and you will be able to enable it.
Thats it, now your display runs at 52Hz instead of 30Hz.