I would run the 4 blade prop...just because thats what was on a P-51.
I can't stand it when people put a 2 blade prop on my favorite airplane..P-40 WARHAWK..I ALWAYS use a 3 blade on mine.
Ineffiecient or not im not out to win a world speed record.
Thats just miy 2 cents
By the way,I use 4 stroke engines on my warbirds.