The question of how much benifit you get at higher rpm in the hover/takeoff regime is complex, and I implore you to not think that what works in one model helo will benifit in another.
These are turbine helo generalizations (hats off to RVDT, who gets it right):
Generally, hover performance (weight for power) gets worse at higher rpm because the drag of the blades increases with rpm and tip mach number. If you are up against the transmission limit, the extra rpm gives you more power for the same torque, but the rotor probably eats some or most of it with that drag increase, leaving no great improvement in lift. Remember, the rotor blade area is sized for high speed cruise, and the blades have far too much lift for perfectly efficient hover, so the blades should be slowed down for optimum angle of attack in hover.
But the higher rotor rpm gives you more transient power during the droop in an engine failure (energy stored in the rotor helps you), and the extra rpm gives you much more tail rotor authority, so many helos beep up for take off because they anticipate the engine failure, and tune the flight situation for the reject.
Follow the flight manual for your type, at all times, and ask the factory pilots (a phone call is always accepted in the TP offices I have worked in!)