AFAICT, Material Test results can weed out obviously bad settings and give you a general idea of the range appropriate for any particular material, but fine tuning requires running samples of the geometry in a particular job on that particular material.
Larger squares will give a better idea of cut settings for larger shapes, smaller squares will serve for engravings, and none can match the details of whatever you’re doing.
I used the tests to get initial Material Library entries, then tweak those entries during subsequent projects. By now, I can start from a Material Library entry for that material, guesstimate the speed for (say) a different thickness, run a test piece, and come reasonably close. Before doing anything where I care deeply about the results, I run a test piece (or two or three) to tune the results for that particular geometry, resulting in Yet Another Library Entry.
Bonus surprise: “the same material” from a different supplier (or even the same supplier who just got a new TEU container from halfway around the planet) can require different settings than whatever you figured out the last time around. Unless you’re in production with consistent materials, expect the unexpected!