20% bonus for 6th member comes to mind but I never did know exactly how that works. I would imagine it has to be 20% per person in order for it to be even remotely noticeable.
Somebody even geekier than me might be able to find the info.
I found this:
http://strategywiki.org/wiki/EverQue...ce_calculation
Looks complicated.... eyes started bleeding..... had to look away.
Let me know if it answers your questions.