The new 90 is slightly stiffer. As stiff as the PS 85. This might be a better way to get more pop on the serve and groundies. I feel the only reason why Fed is experimenting is due to Nadal. A stiffer frame might be better to handle the heavy spiny ball that comes up high on Fed's backhand. I think the bigger headed racket especially anything bigger than 93 hinders feel and precision for ridiculously talented Roger Federer.