How do props relate when you drop the diameter.

on my TTPro .60 I'm running 12 x 6.

on the top flight prop chart, below the 12 x 6 comes the 11 x 10.

If I switched to an 11 x 10 I am now traveling 10" per revolution ( theoreticly (sic)) But I dropped an inch in diameter so how does this 11 x 10 relate to to 12 x 6 ????

Is there an overlap in the performance of the low pitch 12" and the high pitch 11" ?

Steve