Something to consider....

The smaller the displacement the higher nitro content typically. I like 15% in everything up to about a .90. My persoanl opinion. I have found that where I lived and flew all the time, Western Washington (cool and humid) the 15% worked best.

The higher nitro content means higher head temps. After many hours of run time with a given nitro, 15% for example, when you start noticing reduced performance then you go to a lower nitro. What this does is reduce the head temp, meaning that the expansion of parts are less, meaning that you have a gain in compression. This is all taken consideration you are flying an ABC,ABN type, 2 stroke, engine.

These thoughts are for general sport type engines. If you look at the pylon racers, 3d, and heli guys, you will see that they are flying high nitro content. Usually 20% and up.