Do you have any tips?
I generally do 4 frames per rep: an idle, wind up, pump, and return to idle.
The speed is all dependent on what you want to convey. Do you want them to be really into it (9 frames per rep), do you want them to got at an average pace (12frames), or do you want them to take their time (20 frames). Using IK arms can also help as you can lock down the arm to the guy's dick, so at that point, you just need to move the IK arm and wrist rather than moving the whole arm individually