Forgot to mention that piston accelerations also have a lot to do with wear, and that is a function of stroke and RPM. Cam wear is also a function of spring pressure, profile, and RPM. Hotter cams mean stiffer valve springs, and faster valve acceleration, which means harder landing when the valves close, which can mean more wear. Basically, the faster you spin anything, the faster it will wear, and it is not a linear relationship. It is probably more like an exponential relationship, e.g. a motor may wear at rate x at 4krpm, but may wear at rate 4x or higher at 8krpm.