I may be completely wrong about this, but math would dictate as the number of guns increases it would take more and more of a delta to make a discernable difference. If ship A has 3 guns and ship B has 6, ship B has a significant advantage. If ship A has 30 guns and ship B has 33, the difference is negligible. I'm probably wrong, but eventually there is a point of declining returns such that you'd need to increase your firepower by a significant amount to gain a real advantage. If that's the case, I'd expect a graph of guns vs. broadside rating to be parabolic as opposed to linear.