Grav,
The concept is called "aerodynamic blade loading" and is abbreviated as Ct/sigma. Most helo aero books discuss it well, the best is in Stepniewski and Keys, frankly.
The turbine helo power to weight ratio varies from 3 to 10 Hp per pound, a recip never got more than about 1 HP per pound. Thus, the turbine engine was so light, the designer could put on on that was "too big" and reach for speed by trading down hover efficiency for cruise speed. That is why the S-58 has a Vne of 110 knots and the S-61 has a Vne of 144. That jump is purely the product of making the rotor chord match the high speed cruise needs instead of hover efficiency.