Here's a note that was alluded to in the opening post. I don't have a citation on this but I have read that a study was done showing that the length, weight, and weight distribution of a bat do not factor in to exit velocity of a batted ball. In the study balls were struck (I think from a tee) by different-sized bats all set at the same speed and there was no difference in the distance the balls traveled. There are other factors of course, primarily pitch speed, the angle of the swing, and how the ball is struck, but in order to get the exit velocity as high as possible you have to get the bat moving as fast as possible. So it would seem to me that players should use the lightest bat that they can control.