GolfMe: I was playing a R flex shaft in my driver before I increased my swing speed to over 100. At 97 MPH I was doing fine with the R flex shafts. It all depends on how you load the shaft, more so than just your swing speed. If you can, get tested on a ShaftLab and find out how you load a shaft. At 95 MPH, 2 years ago, the recommended flex for me was A flex. I was playing R flex, but A flex is what the recommended flex was. Now I'm at the top end of S flex, with a late release. Top speed now is 110 or 115 if I do every thing correctly. Tha'ts in practice, on the course more like 105 tops. I never seem to do it all correctly on the course for some reason.