With his current style and insane court coverage, I'm thinking his game will start to suffer around 25-6. Not to say he won't modify his game before then to prolong his career. But let's be honest he's breaking down now. I think Hewitt is a ok example of a player that relied on speed as a weapon. Now, that he doesn't have that extra bit of gas it's hard for him to keep winning. Nadal obviously has extra weapons, the ninja forehand and backhand (for that matter). The thing is.. will it be enough at 25-26-27. I'm sure Fed would appreciate a few less balls coming back because of Nadal's court coverage.