Help with 4k Playback on Shield, source too slow

I’m having trouble getting 4k video to play back continuously without pausing and skipping. I occasionally get the message that the source is too slow. Here is a quick overview of my setup.

– Media is on an UNRAID server running plex. It’s an AMD A6-3500, 8GB memory, 3x 4TB WD Red (1 parity).
– UNRAID server is connected by ethernet to my Asus RT-AC87U. My shield was connected on 5g, but I ran a temp ethernet cable and still see the issue.
– Kodi 17 is running on my Shield TV using the PlexKodiConnect plugin. Video playback is direct play, no transcoding (verified in Plex).

I’m not sure where the trouble lies and exactly where to work.

I did test by using SolidExplorer to copy the 4k file to the device to see what rates I get. Speeds are about 6-8MB/s but its very inconsistent and drops below 1MB/s often. I’m not sure if this is a good test to go by or not. Is the Shield capable of streaming and playing 4k over a network? Or is the hardware not fast enough to do this?

EDIT: I also have a sandisk 64GB UHS-1 micro SD card in my Shield. Would it be faster than the internal storage if I moved Kodi to it?