Board Thread:Game Discussion/@comment-158.82.202.5-20130517175624/@comment-158.82.202.5-20130520230741

I've seen a range of 9 to 15 for the ones I've participate in.

I had one where 3 people did about 110 mil. So you can definitely do it with less than 8, but why would you want to? You lose the co-op bonus.