I think, at the end of the day, that you would increase your chances with 6 months payslips rather than 5 or 4 months worth. It becomes more of a risk, the less info you submit. Evidently it is possible to obtain the visas with a more minimal amount of documentary evidence but it can depend on the ECO on the day as to how stringently they may feel they want to apply their own guidelines. It becomes more of a gamble, the less you submit.
Also, the more info / material you submit, the more of a good nights sleep you will get once you have submitted the application.....and before you receive the decision.