Common statistical metrics are not applicable in performance testing. Incorrect metrics may cause you to ignore real problems and to optimize where it isn’t necessary. Let us look at the proper way to do performance testing.
What do buying a fire extinguisher and not smoking inside the house have in common? Both are aimed at mitigating the effects from a potential fire. The important difference is that one measure is proactive, and the other is reactive. Same applies to performance: monitoring reacts to damage and testing prevents damage.