I just got the Tour Version of the X-100 DG's in some Titleist blades... too stiff for this guy. If I go super hard at it, they are fine, but the subtle miss and my fillings shake. Besides, I only hit a couple of "full" iron shots during a round anyway.
Funny, I have the old satin Precision Rifles in my old Titleist blades and they freq out the same as the X-100, but the X-100's feel like telephone poles.
Another odd thing, when I demonstrate something with a students soft shafted club, I really have to be patient in transition or I'm liable to miss the dang ball. Amazing how the shafts provide that sense of timing.
I'm not enough of the shaft nerd to know all the details.