the A20 we have in game is already a stellar energy dogfighter with the lethal .50 package.  Giving her C-hog lethality is the definition of overkill.
4 20mm and 2 50 cal is not overkill.  17.2 50 cal
4 20mm and 2 30mm is overkill.  36.0 50 cal
50 cal = 1.0
20 mm = 3.80
Mg151/20 20 mm = 3.3 
30mm = 11.4
Alright, maybe 17 50 cal is a bit overkill. 
Look at the 110 G2 though.  

That's overkill.
I have no problems with the 6 50 cal loadout but the 20mm just make it so much better. Of course it will come with a perk price, limiting it's usage. F4U-1c levels maybe?
And 8 50 cals would be nice to have too. Perk it at 2 or 3 if it even requires a perk at all.