in a slow target rich situation the spit5 or the a6m2 will earn you lot's...I like the fm2 in slow low weed scraping fights because the Nimble Pig(fm2) is a lot harder to take down than a spit or zero....but the guns are a little less than average, but if you like 50cals....it is a fun ride.
I have also been eny restricted and flown a 109e & F and found they are very capable perk farmers.