I’ve got a N40L running TrueNAS. It is slow for mass transfers but at about 40-60mbps transfer speeds it is plenty fast for file usage (jellyfin libraries etc.) Right now it’s just a secondary but it is quiet and uses little power. You can get 3.5 to 2.5 adapters and use ssds for even quieter use.
In other words don’t be afraid to trawl around on eBay and experiment.
Encryption slows it down a lot. It’s just a Turion II