RE: 5% or 10%
About all you will see between your 5% and A change to 15% is A lighter wallet and an engine that may or may not be easier to tune. In glow engines I operater two strokes from .25 to .91 and then I start getting into my four strokes from .91 to 1.40. I burn 15% in everything. Just because I don't want to have to keep A lot of different blends around. My four strokes run fine on 10% but the more nitro the easier it is to get the low end in tune. The higher the nitro I use the easier it is to find that sweet spot but the extra price I have to pay after 15% just isn't worth it to me, I took the time and learned to tune one. There are reasons to run the higher nitro but unless you live in A place like Denver where there is no air then A sport pilot just needs to get what works for him.