Reading this thread and the advice, I almost forgot this is an "early retirement" forum.
There always a reason financial benefit to work 4 more months? You can't get the time back.
When you have enough and have had enough the forgone income will not matter. Most of us left in our highest paying years. So be it.
I can see where you are coming from. I do think it is different when you are talking four months with a specific and significant payoff. Having said that, it doesn't mean it would be wrong to leave earlier. It's really dependent on how important that extra money is and how miserable the particular person would be staying even a little longer. Only the person making the decision can know how important those factors are to them.
I was in a somewhat similar situation. There definitely would have been a significant financial upside to staying for just a a little while longer and that was my initial plan. But, one of the factors that led me to leave earlier was that there were assignments on the immediate horizon that I didn't want and I knew that the odds were that they would give me more (even if - or maybe especially if - I told them I was going to be leaving in four months). TPTB had a tendency to give me the most challenging, stressful, and time-consuming projects. There were too many colleagues not carrying their weight. Earlier this week, when the market was down, I was thinking that I should have stayed just a few more months. The next day, I saw a former colleague and was reminded that those months would have been miserable. There were reasons I retired early.