The A6M3 turns a bit (about 5-6%) better than the 5b. Do a synthetic test, you will see. Also its easyer to do the vertical hammerhead-style reverse in the 3 due to its better roll rate.
The Brewster... its instanteous turn rate is excelent, just like an A6M3, has smoother handling than the zeeks with flaps, but its vertical performance is limited, also the turn rate is dropping in a sustained situation.