I know a lot of people have referenced the SENG site. My I suggest you pay particular attention to the physical over excitability section. It sounds like your son needs a LOT of exercise and if the aggression is happening while he is doing gross motor activities this could be part of it. Martial arts may be of some help here.

As for the tablet, we have one for DD4 and I would only recommend it if your child has a great amount of self regulation or can be told no. Sooooo addictive. Thankfully DD only asks for it every few weeks so we let her go for it, but really it would be a shame to have a child of any age relying on one as a coping mechanism. If it's mostly for while you were needing one on one time with another adult, maybe some apps on your phone would do the trick? Works for me.