I normally ise 20% Nitro (all synthetic oil) on my YS-110, and I was getting about 9200 RPM with a 15x8 prop on 20/20 fuel.

Today I tried 30% and comfortably got 9800/9900 RPM. That's a 600/700 RPM increase on the same prop (15x8).

I also tried a 14x12 prop and got about 9400 RPM. Not bad.

So there's seems to be a substantial difference between 20% and 30%. The engine also runs a lot cooler (it was already quite cool on 20% nitro; but with 30% its even better and runs smoother as well).

The difference seems a LOT more pronounced on 4-strokes than on 2-strokes. On my JETT 76L, the difference between FAI fuel and 15% nitro is about 1000 RPM at the top end. However, in a vertical climb, the 15% fuel ensures that there's no drop-off in RPM while with FAI fuel this seems not to be true (i.e. the engine seems to lose some power as the load increases due to the climb).

Atul