Posted for "terrence o'neill" <troneill@charter.net>:

 Thanks, Paul,
 An anecdote: for my book GM,DS! I interviewed Chuck Tucker, who lives in
Hollister, CA.  Chuck, with just his brother, himself entered TWO P-63s in the
1946 Cleveland National Air Races-- one in the Bendix and one in the
Thompson....a Race 28 and Race 30.  As and ex-Flying Tiger and Op officer of
the very first US jet fighter squadron, he could fly everything from
everything from P-39s asnd P-40s to the latest -63s, -51s and -38s, and said
the -63 was the fastest at low altitude...so he bought two new ones
war-surplus for a couple of thousand each.  And modified them.  Anyway, he
told me "I don't know where these guys (other racers) get these ideas...
putting bigger props on their planes.  For speed, you want the smallest
diameter your engine and handle."  Chuck had friends at CalTech and at
Lockheed, including Kelly Johnson.  So,
 He qualified fastest for the finals in the Thompson, but had to drop out when
his gear wouldn't come up ... (another story) ... So, smaller diameter for
more speed.  Keep the tips under Mcrit, and more blades to keep down the
diameter, reducing the requried torque to turn it... as you said.
 Terrence