Too many variables...rpm and tune up have a lot to do with it. But here is what I do every 2 seasons or every season if I run it a lot.
Remove all spark plugs.
Leakdown test. TDC. Record % leaking. Note where leaking from. Through intake is intake valve...exhaust, etc..
Now I am picky...anything over 10% leakage and I am going in there. But 20% or more is probably more the norm.
Leakdown test #2. Remove the rocker arms and leak test again. Let the piston push down to bottom of cylinder. Now hold you thumb over spark plug hole of cylinder(s) next to the one you are leaking. Feel air pressure? Head gaskets are leaking between the cylinders if you do.
Remove intake manifold and roller lifters. Inspect them.
Remove oil pan and check bearings. Main concern is always the main bearings.
Not saying that you go to all this...but is what I do.
You don't want to go to all that....then leak it down and then remove the oil filter..cut the oil filter open and look for metal.