Oh sh*t, you're on to me. I don't have a clue what all the various
needs of an engine is, but I do know that the amount of allowable
contact, and the possible film strength varies a lot at different
points within the engine. The metal components will vary too, so with
all these variables there's no meaning behind the question that you
asked. There WILL be metal-to-metal contact in the valve train at
times. Also at the top ring/cylinder. And even in crankshaft to
bearings when lugging an engine.