The 540 rotor system was also installed on the UH-1M and some of the UH-1E's, as well as the AH-1Q, R, and most S's. It was a 44 ft. diameter rotor with a 27 inch chord on the "door hinge" rotor head, and this system was more optimal for higher speed flight. I am not surprised that the Chinook could out run the AH-1G, considering that the Cobra probably had a load of 2.75 inch rockets, 4000 rounds of 7.62 mm, 300 rounds of 40mm grenades and possibly 1000 rds. of 20mm. I flew them in RVN as well as in training and testing in the states and we were always near max.GW. The Vne on the AH-1G was 190KIAS which was only achievable in a dive. Without bullets, rockets, etc.I suspect it could keep up with an unloaded Chinook.