Mart, you say;
we are discussing why Sikorsky opted for a 2 speed control system over continuously variable speed.
This may be a presumption. The statement mentioned by IFMU is "The main rotor will be slowed during high speed flight ..."
It will be interesting to see if the rotors are 2-speed or variable-speed. It will also be interesting to see if the propeller is 2-speed, or variable-speed; or perhaps variable pitch.
Of greater interest, IMO, is the earlier PPRuNe discussion, where the need for rotors with more than one (slow) speed is questioned.
Dave