It's pretty easy to find the general recommendation for flex based on swing speed, but there are nuances, especially at speeds that are on the cusp between two different flexes. Here are some concepts to consider: Generally, players with quick transitions see better results with stiffer shafts and players with more fluid tempo and transition can be better suited for softer flexes. Distance can typically be seen to increase with softer flexes, but timing and tempo are required to keep accuracy. Conversely, dispersion generally decreases with stiffer shafts.