The 30mm wing mounted guns on the fw190a8 have extremely high bullet drop, best used in a top attack against bombers where it shines, it also make the plane very heavy, with a slow climb and it is 30-40km/h slower than without them.
When I was buff hunting i used to come in from coalt position at lower speed from 10 or 2 o'clock and raked the 3-plane formation.
Against Lancaster's you can expect all 3 to go down when you are doing it right, against B17's - you can get one or two, and the 3rd damaged with 4*20mm and 2*13mm. The hard part is to shoot with correct lead.
The hardest bomber formation to kill is the B26 formation, you only get max one, and the other ones slightly damaged, and if you go after them in a tail chase you end up with a kaputt engine, due to the bombers speed, your closure rate us abysmal.
The B26 is the hardest bomber to kill in the game.