Using latest nightly build of MPC-HC x64 from here MPC-HC Nightly Builds you will see CPU usage of almost any 4K HEVC going down below <40% without using HD4600 iGPU (software only solution), with your system (Core i7-4790K)
But the specific files from that page you suggest, it seems to have encoding/muxing problems, because they obviously have a small judder during playback. (a repeatedly spasmodic movement of picture, after a few seconds of normal playback each time)
Try some other 4K HEVC clips or try to transcode/ remux to different formats those clips, maybe using some filters.
Both decoders (Strongene's OpenCL and LAV Video) have the same problem, so I think is the source not the decoders.