The piston issues were and are brought about by bad tuning issues. All the versions of duramax engines have been pretty sound. LB7's have had injector issues and are harder to change. LLY's have been know to run hot when towing in Hot outside temps, LBZ/LMM have had piston issue's from tuners doing the wrong thing. In stock form they all run well. So pick you poison based on what you want. As far as thinking the power is going to be different they are all the same displacement with the same head ports, valves. The compression ratio is lower on the LBZ/LMM but this was done for emissions and the turbo are all pretty much the same for LLY - LMM. Once you start modifying they all have the same potential.