This video provides information when purchasing a stick. Therefore the different sizes and flex. It also shows a graph on height to stick based on your body physique (weight and height). This is an reliable source of information, however I do know certain people who do not follow this rule of thumb, and do just fine. This is something i would like to test too, if the flex of the stick affects the top speed of your shot even if both sticks are the same height. This source will be more a reference when doing our experiment.