That’s a very good summary!
So in a way the optimal texel size is what I was looking for - a way to determine the maximum that is achievable with the source images. I still think that the term “Quality” in this context is confusing. If it were only an image we are talking about, we would not necessarily say that an image with higher resolution has a better quality - we would say it has a higher resolution. Quality can mean much more than resolution. So maybe it should rather be called that? Texture Resolution 70% - everybody could easily guess what that means.