I don't know if any of this will help, they are all so different.....
We've found out that milk pushes our little boy(7) over into similar behaviour to what you describe. We also give him fish oils, which we believe calm him down. I, too, have had to carry him under my arm to the school taxi, he also had to go twice to school in his pj's! All I have to do is threaten this now and it kind of does the trick.
Like you I have a long suffering elder daughter(10) who's hair gets pulled mightily at times.
We don't try to do things with him if he isn't interested any more as this can push him into a rage. And recently we have discovered that time warnings are quite good eg " 2 minutes then put our clothes on" or "play then taxi", and make sure that we say his name and that he has actually realised that we are talking to him.
We really understand how you are feeling. Letting it out here has to help.
Keep in touch