Two other good methods to build the stamina in your fingers aswell as your forearms are 1) It's like a hand grip for strengthening fingers. climbers use it. It has individual springs for each finger and it's resistance training which builds up agility and strength. 2) It's called a powerball, it's about the size of a tennis ball and it has a gyroscope in it. The idea is to keep the momentum going by rotating your wrist and it massively works your forearm muscles.
I have found that both of these are excellent methods for faster fingers for both left and right