Force = mass x acceleration.
This simple formula confuses some people because they assume there is a large acceleration difference between a light, say 19oz cue and a heavy 25oz cue. There isn't. Your arm and shoulder are hardly slowed by a 6oz difference (thats the weight of an infant's juice box, for example). So that's one part of this to consider. The second part to consider is the other side of the equation: the mass involved. There is a large percentage jump from 19 to 25, so the gains on that side of the equation are considerable.
Finally, two things: no pool organization has a minimum weight for the cue used for a break. None. However, they all have maximum weight limits. Why would that be? If lighter = much faster = much better than why has someone not made up a carbon fiber 1oz break cue? And secondly, controlling the cue ball and hit on the break is very important. A heavier break cue allows you to use less force on acceleration and concentrate more on control and a good hit. Try it yourself.