This is probably the best explanation as to why Rafa causes Fed. & just about everybody problems on the clay. If the courts are dry & hard: his spin should be a factor, it is also why if he can get the trajectory right, he gets the depth, then only the very best can live with him.
Because of the higher RPMs he gets more "jump" off the court.
It will be interesting if he gets the same "jump" in the desert at Indian Wells and if he can get the ball fizzing. This will test his knees & also the spin level.
It is literally going to be tougher on his body to create this torque.
On the "other" part of the question: Who knows?
The heaviest part of his balls is that he doesn't fold under pressure when the match is to be won. The other guy has to take it or break him down so that his body & then his mind, will is dissolved.
You have to be good enough, on that day, to do that.
Almagro couldn't do it, neither could Ferrer.
Who is next?