I would think that every rev is doing you damage.
Every engine is made to rev.
My point, every time an engine runs it is wearing out. It is a simply case of friction. The faster an engine revs the hotter it runs the more friction that is created and the faster an engine will wear. You cant relly say that high revs are doing damage, thats what engines do, but it is wearing out quicker than if your didnt rev the engine hard.
Highly modified engines are designed to rev higher, they are designed to opperate more eficently at higher revs, but still the longevity of the motor is sacrificed. Look at F1 engines. One race and they need to be rebuilt.
Every rev is doing you dammage.
Simply, a motor that reves low or is not under much strain is going to last longer than an engine that is reved hard, eg. 250cc generator motor compared to a 250cc motor bike.
However, engines do need a good punt every now and then to circulate the oils and get rid of carbon and oil build up.
In other word I dont relly know what the hell im talking about but it sound good. You decide
Adam