Interesting thread, I was just thinking about this topic this morning. I'm going to update my OLLLLD rackets, and have been looking at the stiffness indexes and trying to reconcile my hitting experience with some of these rackets against their "rated" stiffness. My experience is limited as I haven't hit with a lot of rackets in the very recent past, but my overall judgement is to agree with those who have posted that the stiffness index is NOT a great gauge to judge a rackets overall "flex" or power level.
I'm going to try a little more powerful racket (coming from a RA 60 stick) that is a thin beam construction, so not sure where I'll start.
I will say that the straight beam rackets GENERALLY follow their power levels with the RA index number. Obvious exception to me is the Wilson 6.1 rackets seem WAY stiffer than their RA index number would indicate.
I hit with a couple of Babolats and the Pure Storm (straight beam) feels about like one would think an ~20mm beam racket would hit. On the other hand the Aero Storm is a MUCH more powerful racket, even thought the RA scores are very close or the same.
Only other modern racket is a BB V1 Oversize which has a pretty low RA score, but this racket is a very powerful racket, seems stiff for the whole length of the racket.
Keep the comments coming...