Talking about offline:
I really don't shoot at 400M, but the effects of different MG rounds at that range vary. A .50 cal still packs some punch at that range (that's about 440 yards). A rifle caliber like a .303 has already lost a lot of energy by then. Closer is always better.
I set MG's under 250M usually. With .303's, I set it at 200M.
I set cannon even closer around 150M for "kill shots". The muzzle velocity of cannon tends to be lower than that of MG's PLUS the projectile itself is heavier. Therefore, the "drop" on cannon is higher at a given range. So if you set everything at 400M, MG's and cannon, and fire both at the same time and if both are set at the same "height", the cannon shell should go under the target if the MG's are hitting. (note that I think IL-2 takes elevation into account when setting convergence, however)
Also remember that convergence is your optimum range. At double your convergence distance, the width of the "cone of fire" is the same as the distance between the MG's on your plane. The bullets have already converged and are now spreading out....think of the cone of fire as sort of an "X" if viewed from above. So, effectively, the spread of bullets is still reasonable at double your convergence.
The opposite is also true. If you set your convergence too far out, say 400M, when you get closer to a target your bullet streams will not have converged. You might have to fire at a near target with only one wing's worth of machine guns. At the right angle, a near plane can fly right between your bullet streams.
I am not sure that IL-2 takes "elevation" of guns into account, but I think it does. If I am flying aircraft that fire through the prop where convergence is not really much of a factor, I will set cannons at about twice the distance of MG's. Doing this, it "appears" that the extra drop of cannon rounds is compensated for. In other words, the trajectory of the cannon round is higher than the MG rounds. So if I set MG's to 250M and cannon to 500M, the rounds from both "merge" in height at about 250M. Seems that way at least.
I hope in SoW convergence can be set for each pair of guns. As an example, on a plane with 6 MG's in the wings, you could set the inside pair to converge at 150M, the middle pair at 200M, and the outer pair at 250M (or maybe vice versa). I know in some branches of service the pilot had some options.
I heard a P-51 pilot talking about his preference being for all bullets to pass through one small point at a given distance. He said other pilots liked more of a "spread", but one of his strengths was being a good marksman. In contrast, Richard Bong thought himself to be a poor marksman even though he flew a P-38 and so only opened fire at very close range where he "could not miss". More control over convergence would allow players to tune the cone of fire to their own style.
I have seen youtube videos of IL-2 pilots getting kills on deflection shots at distances approaching 500M. How they do it? I don't know
EDIT: I always fly with overheat "ON" now. It takes a lot more work and I know the AI is cheating, but managing the engine temp is a skill unto itself and, hopefully, will be modeled better in SoW.
Splitter