Alright I agree because I've been using Heavy Duty Balls lately outdoors and they tend to fluff up and slow down the game. The reason why I asked this question to begin with is because I was deciding on going with the regular duty or extra duty balls for outdoor play and now I know the issue I have had with Heavy Duty balls were the extra felt that made the ball fluff up more which slowed the game down.
Also I hear Wilson Balls play faster then Penn balls which could give all courters and serve and volley players a slight advantage. I have tested both Wilson and Penn and I have noticed Wilson Balls play considerably quicker especially indoors.