Hi Guys,
I have experience with the OS140Fi and 160FI. The difference is around +100rpm for the OS160FI.
My set up is a ES composite "2C160S90" exhaust, Hyde type engine mount and 10% Cool Power.
I dont try to get the best power on the ground (shortest exhaust set up) but lets say 100/200rpm lower (around +1 inch)
I like the APC 17/12W around 7800rpm (17/12 is too light for my taste), its really soft in the air with good vertical power and average breaking in the downlines, easy speed management.
I flew the APC 18/10 WNP (7900/8000rpm) at the WC (only on the OS160FI, I crashed the plane with the OS140FI :-( ). Great vertical up and down lines, good throttle management is required.
I tried the normal 18/10, too light with 8300rpm.
About the 15.5/12 4 blades. Good down lines but not easy to go out of the vertical snap.
The Engel modell silence 18/11 carbon prop is too light as well (8300 rpm)

Hope it helps a bit.
2 strokes are not dead yet!

Happy loops,
Benoit