RE: 5% or 10%
You know, I messed around with an OS70FL 4stroke for awhile. It was a real problem. My first 4stroke and it had problems. I had problems too. So I got the 4stroke guys at the field to mess with it. It still ran like crap, so they did all the things they said should be done with 4strokes. One was to run at least 15% nitro in the sucker. It actually ran a bit better. Actually, it still ran like crap, but it did start a bit easier. So there just might be some reason to use 15%.
The experts at my field all seemed to feel that 4strokes run better with more than 10% nitro. So nitro does mean something sometimes. To some people.