Yes we'd all like to know about low rotor speed experiments, but I am REAL suspicious of experienced pilots who are able to take an aircraft to an extreme that is outside the normal operating envelope of the POE.
Yes, I have seen a Robinson factory test pilot take the RPM of an R22 low enough to widen my old eyes but they also know at which point the boom chop occurs from their flight test and computer simulation data. They are thus able to avoid it.
If a totally competent flight instructor chooses to explore the flight envelope beyond where the factory has gone, then he will one day find the aircraft's limitation by trial and error. And then it will be too late.
Please folks, let's not get into macho contests to see who has gone further than the next guy (And it is usually guys who do this stuff...) with his particular machine. Big cohones make big holes in the ground.