The thing is Leanne, it's not finishing at 3am is it? The party ended at 3am (first time round) then, presumably, some people left. So you have car doors banging, tipsy people laughing and calling, taxis drawing up so engines running etc and if it's a 'massive' party (how big is massive BTW) you've got a lot of people coming and going. I can bet that went on for a fair while. So you're probably talking nearer 4am before your neighbours finally got the chance of proper sleep.
Unlike you, who were hosting the party so presumably had the chance to have a rest before it started because you know it's going to go on a bit, your neighbours were possibly working, out for the day, down at the gym or whatever. Then they come home to have a peaceful evening in front of the tv and find this party going on.
Put yourself in their shoes. You're presuming it'll go quiet(er) by 11pm (cos that's what decent neighbours do don't they? Have a look at the clock and think 'time to tone it down a bit now because we don't live in the middle of a 30 acre estate and the neighbours may want to get some sleep'). But the music goes on....and on....and on....finally stops about 3am. So you get down to sleep and look forward to a peaceful rest of your Sunday.
Then mid afternoon another load of people arrive and it kicks off again. You'd presume this was going to go into the small hours of Monday wouldn't you? That would set me on edge for the afternoon, especially if, like your other neighbours, I had small kids who may miss another decent nights sleep because you can't control your friends or family.
As someone has already said, if you don't like the look of your neighbour it doesn't take much to put a note through his door saying you're having a party. BUT, if you were good neighbours, you'd put something like 'it'll definitely be ending by 11pm (or midnight)' and make sure it does!
Your neighbour shouldn't have grabbed your DH throat but imagine your neighbour having a party that went on that long and you're told to 'get a life' when you complain. The next party you'd have I'd be straight onto the police to shut you down before you got going to be honest.
I think it's telling that your other neighbour didn't say a word when the first neighbour insulted you. If I were that neighbour and was intimidated by first one I'd have waited for him to go in and then sympathised with you if I felt you didn't deserve the insult - if you'd have kept me up all night I probably would have been secretly agreeing with him and kept my mouth shut.
Only you and your DH know if you should call the police but it's saying something that your DH felt cocky enough to tell the neighbour to get a life on Monday and is now cowering away from potentially 'winding him up' by getting the police involved. I am reading between the lines that this man hasn't caused you problems in the past but has now snapped and your DH is realising he's over stepped the mark.
Personally, I'd do what you should have done at the beginning. If you can't go round there to apologise for the party (which I understand, I'd feel the same in your shoes), I'd put a polite note through his door. Apologise for the party. He may come round to apologise for the assault. He's unlikely to start any more trouble.
Then, the next party you have, tell everyone - in person or with a note through the door. Put an end time on the notes and stick to it. And don't invite people to carry on a party into two days. It's antisocial. Turn them away or just keep the music off so they clear off early.
Otherwise, do the lottery and try to win enough to buy yourself a house where you'll only disturb the wild life.