Topendtorque:
One minor point - the speed for maximum range in a turbine helicopter cannot be determined in the manner you describe due to improved specific fuel consumption at higher power settings. For a turbine, fuel flow vs. airspeed is needed. To be really accurate in determining best range airspeed for both piston and turbine machines, you should use a graph of fuel flow vs. Airspeed.
Several textbooks make this mistake (but not mine!)