I gave a month notice at my old job so I could close out a project for a client before I left. In the end I don't think anyone but the client cared and it meant I had very little time off before the next job started (three days lol). They also had me train my replacement who spent most of those sessions bitching to me about how he also wanted to leave...
This hasn't been mentioned much in the comments but it's a big factor for a lot of people. You're probably going to have trouble pushing a new employer out much beyond 4-6 weeks. And, has been discussed here previously, there's always some risk that the further you push out a start date, the more chance there is that something could go sideways in the interim. So, if you want to take off 3-4 weeks between jobs, you really can't give too much notice.
