And this got me wondering: Does anybody test to see how high up you
can successfully autorotate from? Is there an actual record for this?

Sounds like a self correcting problem. If you are too high to autorotate,
you will very soon be much lower.

Ummm, yeah, I guess so, but...seriously, is it even possible to try
and keep the RPMs up by diving and turning...I guess WITH the
direction of rotor spin...trying to maintain as much inertia in the
mast and blades before they lose so much torque as to be unable to
provide any lift to pull out of the dive and try to flare close to the
ground? I'm pretty much talking through my hat speculating like this;
I don't really know all that much about helicopters (other than that
I'm not all that keen on riding in one).