Do you run the Beta Plex App on the Shield? (Are Betas Plex Pass only?!)
There were major improvements for the tube and user report that especially 4k is working much better now.
Apart from that, surely the Pro will run smoother than the tube.
Edit: yes betas are Plex Pass only. So you might have to wait a bit until these changes reach the final version.
Edit 2: The latest stable already has this included:
