I'm not sure I understand, what are you trying to do to "prevent cavitation"?

Regarding you rough idle, there may be some variation in the compression between the cylinders, but that's to be expected. I would increase the idle to about 700-750 and see what happens. That fact that it starts easily and run well when warm seems to indicate the engines in good shape. I suppose it could be one injector acting up, do you hear any injector "nailing" when its up to temperature?