i think instead of power, what you are asking is which round delivers the most kinetic energy to the shooter and to the bullet's target
the best idea is to pull up ammo spec sheets for each round from the same manufacturer. take a look at the following links, for instance
9mm:
http://www.hornady.com/store/9mm-Lug...tical-Defense/
kinetic energy = 332 ft lbs
.40:
http://www.hornady.com/store/40-S-an...tical-Defense/
kinetic energy = 506 ft lbs
Chevy Corvette Z06:
http://www.chevrolet.com/corvette-z06/features-specs/
potential energy to drivetrain = 470 ft lbs
therefore:
energy to target and energy from recoil for .40 = 1.52 energy to target and energy from recoil for 9mm
energy delivered from .40 = 1.08 energy delivered to Chevy Corvette Z06 drivetrain
Best Regards,
- MN
