Oh-man, we started the fuel debate again,.......just find a fuel that runs the engine well and fit's your preference and budget. I'll burn a gallon a day running about 8-9 flights on my skybolt or TF P-47, so cost per a gallon is important, on 40 sized planes, performance is more of a factor, so they get the better fuel because I can get twice the number of flights out of a gallon. All my fourstrokes have been treated normally, I forget to put afterrun oil in them every now and then, I try to mix the little bit of old fuel with the new gallon and when I run out of 15% I will run it on 10% for some of my other planes, I just realize that it's not going to run the same as the other fuel and tune it accordingly. I'm more interested in flying on the wing rather than the prop so that is where I stand on tweaking engines to get every last drop of power out of them. The wear of an engine can be offset by running a lower nitro, if compression decreases the lower nitro will make the engine run cooler, this will keep the interfearence fit between the piston and cylinder tighter, hence extending the usable life out of a worn engine, also adding castor will help seal the fit at top dead center. So with that bit of knowledge, if you normally run your engine on 15-20% nitro and decide to run on 10%, imeaditaly, plan on breaking it in again because the fit will be tighter due to the lack of thermal expansion.