OK, I think I may already be on more or less the same page as you are then. I recently made the switch to orca slicer (as should everyone, as I don’t see any downside to it), and running the 3 built-in calibration tests you mentioned did help. I was hoping you might have had some kind of grand strategy regarding the other hundred options, because getting those optimal seems like it could be very time and material cost intensive because the number of potential combinations explodes.
So far, the best advice I’ve read on the topic of the most impactful other PETG settings was written by @djeZo888 in his two posts:
and
He wrote in the first post that it took him “weeks of messing around with settings, going over half a dozen of different brand of filaments” to boil it down to the essential few settings covered in the second post.
A lot of the people who replied after his posts said the advice worked out well for them. I also think it made a big improvement for me too, so I reference it here in case it can help anyone else also.