People who advocate one or the other have no idea what they are talking about. Speed *is* power. Think about it. Aside from any spin and/or elevation, the only quality the cueball can have when it reaches the rack is *speed*.
Assuming a dead square hit on the head ball, and a fixed elevation (meaning whether the cueball is on the cloth or in the air...on its way up or down), the only way to "hit the rack harder" is to generate more cue ball velocity (speed). Assuming your mechanics are perfect, and you can always strike the cueball exactly where intended with perfect timing, then generally the only way to get more velocity out of the cue ball is to make the cue stick move faster at impact. This would require more "power" from the human system that operates the cue (the breaker lol).
Power is the ability to do work in a period of time. Accelerating the cue is work. More power can produce more acceleration over the time the break stroke happens. This *could* result in more cue ball speed, but that assumes that the cue ball is struck in the center, at the right elevation, with peak velocity at impact (good timing), with a straight stroke, etc.
Thus velocity is the *result* of the application of power. Power is in the player. Velocity in the cue ball is what matters when it comes to hitting the rack harder.
Make sense?
(And by the way, this has little to do with a *good* and *effective* break. Hitting the head ball accurately with a good stroke will generally produce better results than glancing off the head ball at a million miles per hour...within reason. For 9 ball you can break great with a decent rack at about 16 mph and up...below that and you probably won't make as many balls due to late drops...In any case, most men can easily hit this speed)
KMRUNOUT