I don’t think overheating would cause random corruptions (it should throttle down when overheating, and then shut down if the temperature gets too high even when throttled, but there should never be an incorrect result of any computation), and surely the RAM will run at the standard 2133 speed on default settings - OP says they reset the BIOS settings to default between CPU swaps.
The thing that’s going to be locked behind the subscription is your ability to watch those files on your NAS through Plex when you’re not in the same network as the Plex server. That’s streaming.
If you only use Plex while at home, you will indeed be unaffected