Thanks Ronski I think "resolution overkill" might suit me down to the ground. I wear glasses for most things but have always found that if I sit close enough to a screen I can focus without glassses, which is a treat for my nose and ears. But it does mean that even with fairiy high resolutions, sitting that close, the individual pixels can become noticeable, particularly with text rendering. Not so, with 5K.
Agreed, I'd expect any panel with the same spec to be pretty identical, and probably come from the same factory. But Apple are also pushing a stand-alone LG 27" 5K monitor in their stores, having abandoned their own monitor branding a while ago. I looked at two of the LGs, one connected to a Mac Mini, one to a Mac Pro. Whilst impresssive, the iMac display definitely beat them both in terms of text clarity which is what matters to me. I can't explain why. Even tried fiddling with brightness and then calibration settings on the demo setups, but was unable to make the LG look as good as the iMac.
If I had a criticism, it is that the iMac display was a bit 'glossy'. Whether that will translate into annoying reflections will remain to be seen.
I'll also miss my old 2009 LG's height and tilt adjustments which, given my 'up-close' viewing habits were very welcome.