The base consumer models from regular brands usually have no write cache and are thus cheaper, and obviously slower, but for data storage that doesn’t matter so much.
But you can also look into 2.5" HDDs if you are looking for power savings and noise reduction over regular HDDs.
While theoretically true, the main bottleneck with Lemmy seems to be the database performance, so with both projects depending on PostgreSQL for that, I somewhat doubt that Piefed being written in Python will have much noticeable effect in reality.