user147 we have similar issues with our 4yo (who is in reception, but very young in the year). He's actually loads better than a year ago, I suspect partly down to his own development and partly down to his baby brother now being a mini person who gives something back in the relationship rather than a drain of Mummy's time (he's 21 months now).
Our terrible episodes are less frequent now; every so often, not more than every 6 weeks-2 months. When they happen, they rumble on for a couple of days. This weekend is a good example: DH and I went out on Friday evening and left the boys with a babysitter (who they know).
DS1 knew this was happening and deliberately kept himself awake so that he could see her. She tried to get him off to sleep but he was too excited (and I think, perhaps a little anxious - tell tale sign was that his asthma flared up a bit, which it often does when he's anxious).
He ended up going to sleep about 2 hours late for bedtime, then woke up when we got home - usually he's a very heavy sleeper. He then woke up again during the night and DH had to go in and settle him.
Got up at 6.30 as usual and by 8am he was completely in bits. DH had said he could have a treat at breakfast time (one of those mini-packs of cereal) if he went to bed really well for the us/babysitter on the previous evening, and he was furious that he wasn't going to be allowed it.
Complete rage, as described by OP and we had to restrain him because he gets into such a state that he wants to cause destruction and isn't careful of himself.
If we move ourselves away/ ignore it infuriates him more and he will come towards us and hit to get our attention. If we take him upstairs he will try to run down again and be in such a state he'd probably slip and fall.
So, we gently restrain. I usually lay a hand on him very lightly - no pressure and if he starts to make a move to hit, kick or run away, then I prevent it. All the time I try to remain calm and repeat that we love him and that he needs to calm down. Can he let us help him? Usually after a while there's enough of a gap in the crying for this message to get through and he will simply melt into my arms and we'll suddenly be cuddling. He's then very apologetic.
We got through the rest of Saturday and then Sunday we pushed him too far in going out to see our town's Christmas light switch on at 5.30 and he wanted every piece of tat/hideous sweet that he could see and cried all the way home because he couldn't have it. We didn't quite get into full-on tantrum, thankfully. Once we were home, we had a chat about it, he calmed down and snuggled into me watching The Gruffalo.
This is a child who is considered to be kind, polite and well-behaved by all outside the house. I attended the triple P parenting course because I couldn't cope with his behaviour in the house last year and everyone who came into contact with him who knew about it asked "why? He's so good!".
One thing I did pick up from the Triple P is that in some ways it's quite positive that he's picked up that there are ways we must behave and that he can stick to that - mostly. It makes sense because he does cry a lot less than other 4 year olds we know and seems more robust day-to-day.
Essentially, though, he's dealing with his emotions in a mature way only outwardly until he comes into his safe space and then every now and again he needs to let off steam with the people he trusts to love him no matter what.
I guess as time goes on he will understand and process things more and the tantrums will disappear (they're already massively reduced in frequency).
Trigger points for us are definitely tiredness and hunger - tiredness certainly builds up in a child - over term, over an exciting period like a Christmas or holiday. We struggle as DS1 cannot nap or he will lose even more sleep at nightime as a result of his daytime sleep. 20 minutes asleep in the day means he will take an extra hour to get to sleep in the evening.
Whether restraint is the right thing to do, I don't know. Triple P certainly didn't answer that, although I was honest about using the technique. I really don't know what the alternative is. We try to keep away from going in to tantrum mode as much as possible; which is where conventional behaviour techniques come into play, but once you're there unless you have a padded room you can shut them in* I feel gentle restraint is the safest way.
*joking! (sort of 
)