I experience stuttering when playing back 4K 60fps footage on my PC (i7 3770 + gtx 980) and my Mac (MacBook Pro late 2015).
The PC’s cpu/gpu/ssd/ram usage is well below 50% when trying. The Mac maxes out (maybe?) the cpu.
I’ve tried VLC, media player classic, Quik, etc but to no avail.
How are you playing back the footage? Are you removing the SD Card and inserting it into an SD reader? Are you playing it back from the camera via USB cable? Are you copying the files to an external hard drive?
The best way to play back footage is to copy it from the SD card to your local hard drive (which is hopefully an SSD) as this will offer the best read speeds. Any other way and you risk bottle necking the readrates which will cause stuttering or for drops in audio or video.