Hi,
Be sure to use HDMI cables that are certified for 4K or you may run into problems per HP internal support staff. You may get lucky using older cables but then may be not.
Most of the high graphics cards and high resolution monitors support Display Port. I am using a Display Port cable with my 980TI to a 144 mhz monitor and can be O.C. to 165 mhz. No problems so far.