Differs on how the armament is installed friend Dedalos.
In AH1 I didn't notice any difference between wing armament and nose armament, with the exception of the P-38L and Mosquito, or a plane like the Bf110.
However, there's a significant difference in AH2 now. Countless times I've been shot down in HOs where I was in a wing-armed plane with superior firepower, whereas the enemy was weaker in firepower but had a center-line nose armament.
I've seen you flying the P-38L often, which probably means you don't really need to set convergence on anything. With such centerline armament as long as you aim it right, it will hit regardless of how you've set the convergence.
However, in wingarmed planes - typically those with multiple HMGs set on the outboard of the wing, it depends a lot on your style of fighting. If you do a lot of close-quarter fights and rely on concentrated firepower in snapshots I recommend something around 250~350 for all guns. Those provide you with good firepower in close ranges - but in those long shots against extending enemies over 400yards, or a HO situation it sucks.
However, if you rely on long tracking shots and leisurely BnZ passes something between 300~450 might be better. Longer convergence also helps with HO situations a lot better than shorter ones.