Okay, fought a headache long enough to take at least one look at it, sorry to hold back on ya brah

One thing about your empirically measured tiers I've noticed is that they closely correspond to the timing of "frames" (this makes a lot of sense if you understand a little about graphics programming / game development; it is possible but unusual to handle input at higher frequency than your display refresh rate, so obviously they're not keeping a running tally of how much frames have robbed us, but are instead rounding each time).

That is, you have:
354-360 at 2.511–2.513 → 151/60 = 2.517,
361-386 at 2.497–2.501 → 150/60 = 2.500,
387-439 at 2.482–2.485 → 149/60 = 2.483,
440-492 at 2.461–2.467 → 148/60 = 2.467,

and so forth. Two layers of rounding, yech!