promoting seems to be based on number of wins, unless you outright win your league championship. with two guys ahead of you in # of wins in your division I'm not sure you are a lock to promote.
In any case, it is better to be #7 in a div 4 league than #1 in a div 5 league. tons more money, more competition, and a lot more challenging. Last year in div 5 i could go weeks without checking my team and still win, now I have to put thought into it....and am only .500 this season.
also, i think i only got 200k for promoting not 500k