The actual problem for me of having 6 is a question of difficulty/rebalance, still not answered sufficiently in hundreds of posts. The most common answer seems to be, "let difficulty as it is" and use the usual settings (like Story Mode, Easy, Classic, Hard, Masochist, Real Man, and so) to overcome the consequences of having 6.
Split exp.
Adding more party members doesn't decrease difficulty linearly. Some encounters could be trivialised just by having more tools to play with. An encounter made for a 4 members party simply isn't designed the same way as an encounter for 6.
