" I wonder what the actual RPM limit is on the rotor head before the bearings explode into tiny fragmented pieces of shrapnel,
precise failure-values are pretty much impossible to determine, especially if you consider metal fatigue. Take a batch of 10 brand new rotor heads, and maybe 8 of them explode at 120%, one at 115% and one at 125%. Take the same batch but use them for 1000hrs before the test, and you might get completely different results, who knows!
The manufacturers are smart enough not to let anyone see those kinds of tests. Their job is to come up with numbers that gurantee an explosion-free component life for every single part they make.
And why did we get to see the wing deflection tests on airliners? Probably because passengers got scared looking at the moving wingtips, thinking it's about to fall off.