likewise, no one would drive their own car just like WRC players if you want it early retired. Same for the engine, decreasing the output in purpose would protects the engine and increasing its life. I have a DL50 and always keep it under 6400-6500 RMP with 22 x 8 prop, so far i didn't find any problem with it. Except for extreme use, like match or championship, otherwise it's unecessary to lean your engine too much only for daily fly or practise.