If you are on HDD then looking at what else is using the same disk, and reducing that usage, may yield some results. Forexample, if /var/log is on the same disk and can’t be avoided, then reducing log volume or batching writes may reduce the “context switches” your HDD has to do. There should be options for I/O limits/throttling/priority in systemd. If you have only postgres on the HDD, I’d consider giving it 90% of the max bandwidth – maybe that’d be more effective than going full throttle and hitting the wall. If you have postgres and some other service fighting for the HDD’s time, these limits could help. Make sure access time tracking is off (or set to relatime).

In general I agree with you, especially on the image part, but I found the opensuse page to be a decent variation of this.