You've just made me think about something Von. Scrap talks a lot about the eyes slowing punches down. The acceleration may not be constant throughout the delivery of the punch because on a subconscious level we could tighten up too early. Firstly because we're conditioned to get the hand back quickly and secondly to protect it from injury.

What do you think? Finding out if the punch slows down at all before the target might be useful in finding the peak velocity.