RE: 20% fuel vs 30% fuel
First off, not all engines are designed to run well on 30%. The Savage 25(I'm not sure about the other models) is only supposed to be run on 20%-25% nitro. You could run the engine on 30%, but there may be some more severe longevity issues than running a lower nitro %. In any engine, even if it states in the manual that you can run 30% in it, 20% will still allow you longer engine life and good performance. 30% is for when you want max power out of your engine, and is mostly reserved for more race oriented engines.