In my opinion in AH2 setting guns all to the same range is best. The reason being the air to air shots you will be taking will be within a very narrow range and very consistantly within that range (d400'ish). In AH1 there was some benifit to the 'cone of fire' principle of gun convergence as the range of viable shots was rather large (D200-d1000). So, single point convergence works better in AH2 IMO. The only exception would be if you were flying a plane with two or more gun types that you planned to fire independantly of one another with entirely different ballistics and therefore effective ranges, such as a LW plane like Fw190A8, 109 or 110 with MG's, 20mm and 30mm cannons.
Zazen