I recently purchased a 716 AP1 iron set with XP90 S300 shafts. Since the set didnt come with a 3 iron, my brother let me have his. The only differnece is that if has a regular flex graphite shaft. I was tempted to switch out the shaft but I played a round with it and it feels different than stiff but ball flight and distance seem to still be there. What's the real difference between regular and stiff if they both seeminly give me similar results? (Club head speed is about 101-105)