FED,
You are not comparing apples with apples there. 87% Q at 100% RRPM (N2) and 107% RRPM (N2) ain't the same. The torquemeter only reads correctly at 100%. By adjusting the RPM and considering that the M in RPM = Minutes and Power (not torque) also involves time you are in fact using more power.
The reduction in the fuel flow would be from an increase in efficiency in the power turbine and an increase in efficiency of the gas generator up there where the curve is pretty steep considering the size of the engines. i.e SFC. (Which is why they are small in the first place)
As to the original post, never really thought about it as most helicopters have a pretty small RRPM range power on, thats where it stays. An increase in RRPM will occur in increasing forward flight at a fixed power input but as RRPM is usually constant it would actually be a decrease in power. Otherwise we are just talking about the "bucket curve" here aren't we? i.e. in forward flight until drag becomes a factor the rotor is "less inefficient".
I am assuming of course we are not referring to some aircraft where it is adjusted automatically - EC145, EC135 (not all) ...............................