Power isn't nearly as important as full contact on the one ball. Pros generally break in the 20 mph range. The fastest breaks are just over 30 mph, but you'll never see pros breaking that hard because of a loss of control. You should break only as hard as you can control.
That caveat being given, I'm going to share some tips on generating power on the break.
In baseball, faster pitches are generated with the legs, not the arm. Faster bat speeds are generated by the hips, not the arms. In basketball, longer jump shots are generated by the legs, not the arms. In golf, faster club speed is generated by the hips, not the arms. So what does this mean? It means that transfer of body weight is far more important than arm speed or strength.
Bustamante, Archer, and Pagulayan can all crush the rack. None of them are built like a Hercules. How do they break so hard? They're masters of weight transfer. They generate power by transferring their weight from the back leg to the front, which is why you see a lot of players' back legs fly up off the floor when they break. The best demonstration of weight transfer is simply to lift one leg off the floor. The leg which remains on the floor MUST have all the weight on it.
There are a few techniques which can be used for weight transfer. One technique is to rock back and forth. This accomplishes the task of transferring weight from the back leg to the front leg, but it has a big downside. That rocking can cause excessive head movement, which decreases accuracy. It can also cause the bridge hand to move, which also decreases accuracy. Some players will actually lift their front legs before the final stroke, causing weight to be transferred to the back leg, then stomp that front leg down on contact. Once again, I feel this is excessive body movement, leading to decreased accuracy. I feel the best method of weight transfer is through rotation of the hips. Ask a golfer how they generate club head speed, and he'll tell you it's in the hips. The same thinking should be applied to the break shot in pool. For right-handed players, the normal stance has the left hip slightly in front of the right hip facing the shot. The break stance should have the left hip well in front of the right hip, allowing the hips to rotate through the break stroke. My personal technique has my hips almost in line with the cue as I address the ball, which means that the position of my feet is a little different on the break shot. Instead of having my left foot at a 45 degree angle with the line of the shot, it's pretty much in line with the shot. This requires lots of flexibility, which is another thing those power breakers have in common. I shoot normal shots with my chin on the cue; on the break shot I raise my head about 6" above the cue.
