Also, when using the level up option in co op( 0 ) the other person will instantly be leveled to 50. whereas 9 just gives a little Exp each use.And the Gold Key option works for everyone.You have to be the host for all this to work.Also, not everyone cares about Inf Ammo, but the other 1s may be a problem if you dont know the people.
[Edited by DigitalIP, 9/23/2012 12:59:33 PM]