hi there, I've already learned what the balance point of a racket can do. but what is the exact function of stifness? I'm still growing in power, and my racket dealer advised against me using a very-stiff, since it will soemhow limit me in my stroke, i guess... and another Q is: for power should on always try to go as stiff as he can? (i mean: if i ahve the skills i can get more power out of a stiff, than a medium?) and: hwo does the stiffness of the at500 compare to any of the NS's?