Good question. If you have a look at the CPUs the likes of Synology use for full on media servers like the DS216 Play, then it’s nothing fancy. The DS216 Play uses a 1.5Ghz dual core ARM but with a transcoding engine. It’s predecessor the DS214 Play had a dual core with HTT (4 threads) Intel Atom CE5335 but again that has a transcoding engine.
There is a Plex article thats says for each single 1080P transcode you need 2000 passmarks. Your 5350 scores 2597 so if it’s struggling we clearly need more. That rules out the SoC Pentium / Celerons so you need to look at the socketed processors.
The cheapest £30 Celeron G3930 is 3097 so not a huge step up. A £40 G4400 is 3597. I’ve used loads of these in office type PCs and they fly along. For £80 you can get the G4620 which uses HTT to deal with 4 threads. That has a passmark of 5263.
EDIT Plex TV article says minimum of an i3. What I don’t know is how old that article is as a modern i3-7100 is easily on a par with the previous generation i5.
Reading further, if you have an active Plex Pass subscription for the Plex Media Server account it can use hardware accelerated transcoding. As the G4400 has Intel Quick Sync Video I personally would be willing to take a punt on it but the G4620 would be the safe choice.
Problem is with a basic kabylake mobo and 8gB DDR4 that’s going to cost >£200.
.
