Since Linux 5.2, there is a new metric in the hood: Pressure Stall Information (PSI). Currently it supplies 3 ciritical metrics from kernel: CPU, IO and memory. You can find the values simply by looking to files under /proc/pressure folder. I am not going to try explaining it in detail, since this page already does that pretty good. I've found it way better than just the load metric because of granularity.
I should use this blog more. Here is one of the things might be useful for other admins I wrote meantime. This script generates a report, which includes all important information via ILO interface on HP servers (using python-hpilo package). Supports ILO2-3-4, which is a pretty good range for non-ancient servers I think. I've started to study golang as hobby, so might port this to Go later. But for now, this is really handy: