I don't even know where to begin with this one. I suppose an engine would last the longest at the rpm point at which its oil pump was most efficient, and the most ideal conditions of heat and oil pressure were attained. This is going to vary from engine to engine. Higher than optimal RPM's would not be a better condition IMO for friction between cylinder walls and rings. A motor that cools efficiently and has sufficient oil pressure at 3k rpms is not going to experience less cylinder wear at 20k rpms, even if the rotating assembly could handle the stress.