One thing - If you have a worn cam lobe, there won't be a significant
loss of power until a very substantial percentage of the lobe is worn
away. I'd think you'd see metal in the filter, too. I know of an
O-320 H engine that had a pair of intake valves that hardly moved & the
thing did seem "kinda weak", but still ran fairly smooth.

Sounds like you've covered a lot of the bases.