Hi S.C.; As one who has been doing this since the mid-late 30s, although I didn't hit glow stuff until '45, over the years it has been my experience that for sport , non-racing use, 5-10% is generally ideal. The principal value to the sport flyer is in smoother, more reliable idle, and smoother acceleration. When you talk 30% or more, that's racing fuel, and heat becomes a problem. The basic non-nitro fuel is a good basic fuel for all around use, and usually the most economical. My personal overall choice has been 10% nitro. I don't race, but I like reliable idles and smooth acceleration, and this does it for most engines. With 4-strokes, 10-15% is recommended, as that in-between cycle likes to cool the plug somewhat, and the nitro fuel ignites a bit faster. But try fifferent fuels in the 0-5-10 range and see which your engine likes. THAT is the real proof of the pudding! Sincerely; Lee Robinson ROBINAIRE, W. Palm Beach, FL.