Daniel,
The principle reason for implementing a propulsor is to increase the cruise speed of helicopters. Current rotorcraft have essentially reached the limits of compression on the advancing tip and stall on the retreating tip. In addition, these faster rotorcraft, such as the X2, will have; twin rotors, a wider chord and slower rotor rpm.
It would be interesting, but probably not practical, to see how much a helicopter's cruise speed might be increased by; including twin rotors, increasing the chord, reducing the rotor rpm, pitching the mast angle further forward but not including the propulsor.
Dave