I got my hands on some "civilian" Carburetors for my Sportsters and went on a prop testing spree.

74*F/64% humidity, 5%nitro 25% castor, McCoy MC59 plug, APC Props, factory sportster muffler.

11x8 11,700/2,400
11x9 11,600/2,280
12x6 11,550/2,300 (12,000 open exhaust)
12x7 11,100/2,100
13x6 11,100/1,950
13x7 10,600/1,950
13x8 9,900/1,800