I was wondering if you have an easy way to measure and plot the impact
in page load time, perhaps using Navigation Timing data?

+10^9. I was rather excited to see ulsfo back up and I tried to quickly figure some correlation out of https://gdash.wikimedia.org/dashboards/frontend/ , but I failed.
I think what's needed here is mostly some brilliant idea on how to visualise / graph the data available there by region (and maybe also by project / kind of editor e.g. unregistered vs. registered vs. sysop) without making thousands graphs for each of the combinations. Or just one graph for the region moved to ulsfo to start with of course. :)