I ride .9/.6/.9 4130 (SLX by any other name, without the rifling) in a 63 cm. frame. I have even used .8/.6/.8 in some of the main tubes -- and I'm 200 pounds. All of this does result in a flexible frame, which I enjoy. But if I were racing or even "performance" riding -- as opposed to the purely "smell the roses" riding that I do -- I think the flex would be obnoxious.