You can make adjustments to the blades that are being used on the helicopter you are flying.
In the aircraft editor.
Airframe/Fuselage/Heli-mechanics/Main rotor
In the parameter dialog "Blade Type" click on the blade name and open the rotor blades menu.
You can copy the existing blades you are using, rename them, then edit the renamed blade.
You want to edit the "Drag Coefficient Adder".
An example would be the Synergy N5C value is -.0035. You will want to stay around -.0045 to -.0025 or so. -.0045 is probably what you are looking for.
You can also adjust the Drive train Efficiency(%) on both the Heli-Mechanics and the Tail Rotor. Changes to these values will effect smaller 450 helicopters greatly.
Thanks,
Chris McVey