TT F91S running 10% Wildcat 18% syn/castor blend
Zinger 15x6 = 8200 rpm
Zinger Pro 14x5 = 9700 rpm

OS .91 Surpass II running 10% Wildcat 18% syn/castor blend
Zinger 15x6 = 8400 rpm
Zinger Pro 14x5 = 9500 rpm

Both engines are still breaking in and running rich. Each has about a half gallon through them.
The OS seems to like the 15" prop better than the TT.
The TT turns the 14" prop better than the OS.

I will get an APC 14x6 or maybe a 15x4W and see what I get.