Re: At what speed do you need an X-stiff shaft?My driver speed is 110-112. I just switched to an X in the Proto "ByYou" shaft from a S in the same shaft. I love it but the S wasn't that far off. I still have S300s in my irons and an S in my three wood. I have tried a few other Xs in previous drivers and they have been too stiff. You probably don't need an X. A few key points to remember are: although swing speed is one factor, if you have a quick transition at the top of your swing, you might need a stiffer shaft, and, every manufacturer's shaft flex is a little different. one's stiff flex may be another company's regular flex. also, if you take ten of the exact same shaft, they all may be slightly different. You can check shaft stiffness on a deflection board. my theory is if you find a shaft that works, don't break it.