30hz vs 60hz 4K output I am currently using a MacBook Pro 13" 2015 model with a Samsung U28D590 UHD display.

Currently I am using the HDMI port of the monitor with a mini-displayport to HDMI adapter and receive 4K 30hz output. The display is kind of laggy at the moment, with noticeable input lag with the mouse being the main issue. 

When I switch to a lower resolution it returns to 60hz output and it is much smoother (less pixels) and the mouse input lag is gone.

My question is if I just use a displayport cable and receive 4K 60hz output, will this input lag disappear?
Most likely, yes. The only caveat being that OS X 4k @ 60hz support has been buggy for all of Yosemite.

You'll need a high quality Mini-displayport to Displayport cable. Look for DisplayPort 2.0.