Question for you blokes that have different convergences for cannon and MG's..... WHY??? 
Its preference really, for me it doesn't entirely matter the convergence unless its a 30mm or 30 cal which I keep rather close, everything else stays around 350.
Problem is people have a bad tendency to shoot to far out and not conserve ammo, keeping your converg close and take aimed shots is what makes a huge difference rather then setting a convergence.