No, actually.
It is true that the power button changes power settings from 400 to full (507) hp in the BMW
M5, but this is NOT the case with the X5M or X6M.
I quote from the Supplementary Owner's Manual:
M Engine dynamics control/POWER
With M Engine Dynamic Control you can influence how
sporty the reaction of your vehicle to accelerator pedal movements is to be. Two programs are available to you.
The "Efficient" program is activated after each engine start.
"Efficient program
In the "Efficient" program, a lower fuel consumption is achieved. The engine and the M Sport Automatic transmission
respond to accelerator pedal movements with an emphasis on comfort, which is ideal in city traffic or in snow, for example.
"Sport" program
The "Sport" program permits the engine and the M Sport Automatic transmission to
respond more spontaneously to accelerator pedal movements. The acoustics of your BMW X5M/BMW X6M become more sporty.
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There is NO mention of increasing any horsepower. The accelerator pedal simply becomes more "sensitive" to smaller increments of pedal movement - as it was with the e46 M3, and as it is with the e9X M3. The throttle sensitivity changes - NOT the amount of power that is made available.
I tried a few 40mph to 100mph runs (closed circuit of course
) using both modes. Times were all virtually identical.