Not sure what the stiffness rating on the frame is, however, it feels nowhere near a 71. Not even close. I think the open string pattern makes the head feel flexy/cushiony even with a full poly stringed. This is one of the more surprising aspects of the frame,,,,, how comfortable it felt.
Someone asked a question related to the frames ability to produce spin with something other than a poly. Please remember that spin is generated by techinque and could be magnified by a string or frame. That said, I could almost guarantee this frame will produce more than other racquets regardless of string.
Roger Federer Pro Staff 97 Play test video