Morning 
Wired speed: 10 Mbps - 100 Mbps - 1000 Mbps ( 1 GbE) - 10 GbE . There is no 350 Mbps speed. USB 2.0 will do about 350 Mbps avg, 400 max.
There’s no mention of subtitle usage. Subtitles, being a single-threaded task, show up pretty clearly on CPU utilization graphs. If subtitle burning is active, it’s not uncommon to see a single core fully utilized (25% for a quad core without threading, 15% with).
To diagnose any performance issues, additional info is needed.
- XML of the video being played (so we can see what PMS is dealing with)
- DEBUG logs of the playback event.
a. Start playback
b. Let play for 30 seconds
c. Stop playback
d. Allow system to quiesce
e. Download Logs
f. Attach ZIP
