The measurable "power" of your bow - it's total kinetic energy output - ultimately depends upon just two variables: the mass of the arrow and the speed of the arrow. Kinetic energy of an arrow can be found by using the formula KE=(mv²)/450,240 where m = mass of the arrow in grains and v = velocity of the arrow in fps. If your bow setup ultimately shoots a 400 grain arrow at a respectable 250 fps (a typical field-output for a modern rig), your actual kinetic energy or "power" will be:
Gold Tip recommends, 55 ft-lbs of Kinetic Energy would be sufficient for most popular North American Game Species.
Remember, bowhunting is a traditional and challenging sport. Regardless of how you evaluate your numbers during pre-season, you can't avoid the elements of chance during the actual hunt. Shooting a live animal in the woods is quite different than shooting a block of ballistics gel in a laboratory. In the field you'll encounter unpredictable and complex variables that limit any mathematical model to just a "best guess". If you consider that your arrow must arrive on target then pass through layers of hair, hide, muscles, bones (perhaps), and a host of other tissues and that all of this is happening in an uncontrolled outdoor environment.
As many experienced bow hunters can attest, just as it's possible to make mistakes and get lucky, it's also possible to do everything right and come-up empty handed. That's just part of the sport. With good equipment, good technique, smart planning, you can surely tip the scales in your favor and maximize your chances of success in the field.