Stop partitioning his behaviour. You are doing it already by saying he would make a fantastic Dad except for this. You have to start looking at him as a whole, and accept that these rages are part of his personality, most likely permanent. Upbringing can affect people, but there's good evidence now to suggest that nature, rather than nurture does count a lot more than people like to think (because by believing the nurture theory, it gives people a greater sense of control than they actually have over personality). That means that if the father was a neurotic, depressive, angry, anxious, violent asshole, there's a good chance those traits are inheritable and if the childhood environment was also bad, those traits traits are much more likely to come out. Good luck trying to reverse that.
The worst rage was when i was sat at the top of the stairs and he ran along the corridor as if he was going to push me doenstairs but he didnt, but i genuinely thought he was going to. He said later he would absolutely never hurt me, and if i thought he had the capability of hurting me i should leave
That is fucking awful. He knew exactly what he was doing there - terrorising you. He is raging like a 2 year old toddler, except he's a fully grown adult, a male who's stronger than you. If you have a son with him, expect to deal with 2 strong out of control people, not just one.
You cannot have a normal, functioning relationship with someone who gets this angry. What you also need to consider is that some people are very aware of the effect their rage has on others and they use that fear as a weapon that shuts people down. They don't want to be challenged. Read what @Bunnymumy said.
There are other men who have less control over it but it hardly matters. All it means is that they have not progressed emotionally since the age of 2, usually the failure of parenting or an abusive household. Sorry, but you cannot undo that yourself.
Being able to argue with someone is really important. It's how you get your point across, how you defend your self, how you work things out. If you think someone is about to turn into The Hulk, how on earth is that dialogue meant to happen???