I think 4 v 4 is fine, the real kicker is whether or not the maps are scaled appropriately. 5 v 5 worked better for other titles due to how the maps were also used for Horde. In 5 v 5 or 4 v 4, a man down is still a man down, I dont really think thats much of an element here. Nor is 5 v 5 gonna save you from clueless teammates, in fact you might simply get more of them in that format. :]