Over training the biceps can slow down progress in the entire upper body. When the biceps are tired, they can't be fully available for heavy back movements. This fatigue can create weaknesses and cause the back to lag in overall development. I came to the conclusion that the bigger and stronger I got from training, the more rest I required for my biceps and back to continue growing. Make no mistake.
Recovery is the key to growth in any body part, particularly as a person progresses.
That may mean skipping arm workouts every other time you train, or even more often than that. Back off the 9 to 12 sets total and do fewer days of biceps training over the long haul. I never believed it then, but I can see now it makes a lot of sense. It also explains why people tend to over train their arms, as they become larger. My biceps-training nowadays is pretty simple.