I've seen a lot of threads on how the same model of racket vary in weight, balance, and swingweight. Do they also vary much in terms of stiffness? I have two prestige mids which I have matched up weight and balance wise, and feel about the same when swinging them. However, I can't get the same power or feel when I actually strike the ball. The first racket has a lot of power and vibrates a lot. The second racket is underpowered and has a "plush" feeling to it. This makes me think that the first racket is stiffer while the second racket is more flexible. This has been bothering me for a while now. Anyone else notice this with their rackets or am I losing it?