Don, you legend! Thanks for such a comprehensive and thorough reply. Makes total sense! :-)
I know manufacturer's specs are rarely accurate, but there are independent grass-roots comparator sites for camera lenses, such as
this one.
I wonder if there's anything like that for EP's? Or are the lab tests for camera lenses more affordable/widely available than for eyepieces? I guess one difficulty is that any eyepiece is going to be working from the light off an objective lens/mirror which would either have to be optically perfect to begin with, or standardised in it's imperfection across multiple repeatable tests in different locations.
Hmm, interesting to consider, anyway :-)
-Markus