The simplest way to measure impact on users would be to just use boomerang which gets you all of this out of the box: https://github.com/akamai/boomerang

To do it yourself, you need a combination of PainTiming and measuring LongTasks or study the periodicity of setInterval/requestAnimationFrame

The above works for synthetic as well as real users. If you're able to measure real users directly, then you'd also want to look at Input Delays, Rage Clicks, Dead Clicks, Missed Clicks, Scroll Jank.