Xeon E3-1260L for Plex transcoding

There’s a discussion on hardware transcoding that will probably answer a majority of your questions if not all.

Transcoding 4K takes a lot of resources, so it’s recommended to not advocate for it. Direct Streaming and Direct Playing 4K is fine and can be done on practically any recent generations of hardware.

In terms of being better than Synology, that’s a very low bar honestly. Practically everything recommended here as a NAS will outperform Synology.

So swing over to the Hardware Transcoding discussion for more answers to your questions.