The P-61 was one of the tightest turning American fighters. Clean bird, no flaps, it would outturn everything on the U.S. side except the FM-2 and P-63 in real life.
Top speed wasn't all that great, but it was faster than the Wildcat and about on a par with the P-40 Warhawk. Diving speed was fantastic. Climb speed was slow.
If introduced to AH...it would catch a fair number of people by surprise. Well-flown it would hand many a cocky armchair fighter jock his head.