Hi!
There is also the problem with a full size 2 blade prop that the tips might reach super sonic speed...ever heard a AT -6 with it's direct drive 450hp Pratt & Whitney rew up [:@]
But for most models a 2 blade prop will out run and out perform a 3-or 4 blade prop. We don't risk our prop tips to reach super sonic speeds.

Regards!
Jan K