One thing I noticed was Fed's racket speed is a bit faster using the new racket. I believe it's cuz either: 1. He did strength training for his arm during the off season and he's generating faster racket speeds now. 2. He uses a new custom that's a teed bit lighter ( I believe this is so) 3. It's cuz of the pj and it's the colours playing tricks on the eye that his swing is faster But i've done some comparison and i really do believe it's no.2. What do you guys think?