Yes, there are may variables that effect the life of an engine, proper breakin, contaminants in the incoming air, contaminants in the fuel, amount of oil in the fuel, initial piston/liner fit, metalurgy used in the piston/liner and how lean the engine is run to name a few. Some factors such as dirty air and lean run can kill an engine very quickly, others will do the job more slowly. The differance in wear between using 20% fuel and 30% fuel is one of the miner wear factors, simply because there is not that much more power produced with 30%. If all other factors are kept constant, I still stand by my statment. Any thing that increases cylinder pressure will lead to more wear of the piston liner on the side opposite the crank throw and will increase the pressure on the con rod bottom end, also causing wear unless plenty of oil is used in the fuel. There are only two ways to increase power, increase cylinder pressure and increase RPM. Race engines do both, that in why they are worn out in only a few hundred miles, whereas the street engines they are base on may last a few hundred thousand miles. A pylon racing forty that is raced every weekend will not last for years like a sport forty that flown every weekend. With power comes a price.