I will probably regret this as this seems to have become quite a heated thread and I have only just glanced at the end. Feel I ought to chip in on something DM just said :
"Rotor control when power off can only be controlled by aerodynamic means, but to change that means a change of blade characteristics, however in the case of FLynx the customer hasn't requested that to happen so for good or ill it is what it is."
Absolutely correct but this is surely only part of the problem. Also of critical importance are the flying control mechanical characteristics used to control that Nr and the presentation of rotor speed cues to the pilot, be they visual, audio or by other means. You will never make a silk purse out of a sows ear and sometimes I wonder if it is worth the bother but there are often multiple solutions that can go into mitigating a particular problem.