I just received the Dell 24" 4K monitor I ordered in anticipation of receiving my new Mac Pro. I hooked it up to my MacBook Pro via HDMI and calibrated it with an i1Display Pro. The images displayed on it are ASTONISHING. The pixel density (184ppi) is very high and it displays 99% of the AdobeRGB gamut. (The MacBook Pro 15" Retina display has 220ppi and maxes out at 2880x1800). It's running at 3840 x 2160 at 30 Hz via display port right now. Perfect for photo work.