Lots of folks are trying to run HDMI for 4k at 60Hz. HDMI was never originally intended to go that fast. It was built for 1920 by 1080p.
The "electrically-equivalent" DVI supports wider displays by adding three more color signals to its interface to reach display widths above 1920 wide. This is called Dual-Link DVI, and it requires the extra signals (and special cables that carry them) to get to those wider widths. Otherwise the signal speeds (to get that much more data onto each screen) are on the verge of impossible to create, run across a cable, and receive -- they are just too fast.
You can sometimes push HDMI to do 4K at 60Hz if absolutely everything breaks in your favor. The right interface, the right cables, the right settings in BOTH the computer and the display. But it is far beyond the way this interface was originally intended to work, and despite doing everything "the right way" sometimes it just does not work.
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DisplayPort -- both Mini and Full Size variants (which differ only in the size of the connector) was designed from the ground up to run at faster speeds like 4K at 60Hz. The signal levels use lower Voltages for faster switching times. Most of the signals, and especially the color signals use push-pull drivers and receivers for low noise at higher speeds. And once the screen has been painted once, only the changes are sent across the cable, reducing the data rates required.
The downside is that a DisplayPort display requires a screen buffer in the display. So the displays may be a little more expensive. But the results are far better, without having to fiddle with it.
executive Summary:
If your display has a DisplayPort option, do not struggle with the multiple hacks required for HDMI. Go directly to DisplayPort.
