Hello Drew,
Henning - about all I can say is that you still need to think of the lock and key relationship to the question. How does a particular paper "see" the dye clouds of a particular film,
the main influence of the paper is the colour rendition. But that wasn't our topic here at all. Whether you do like Ektar's colour rendition, or the new Ektachrome, or Portra 160, or Provia, Velvia etc. and how these are influenced by different papers and their colour rendition, is
- a matter of taste and therefore extremely subjective (ask 10 photographers about colour and you will get at least 12 different opinions....

)
- a matter of your target: What specific look do I want to get as a photographer or artist for a specific photograph.
Therefore the best solution = fulfilled aim / the look I want may be in one case Velvia 50 on the new Fuji Maxima, in a different case Portra 160 on Endura, in a third case Provia on Endura and so on.......
But papers don't physically change the objective detail rendition (sharpness, resolution, grain) of the film. The only significant influence can be a bit higher subjective sharpness impression/look by a paper with higher contrast.
Just looking at spatial frequency charts doesn't tell the whole story,
Exactly. That is what I am talking about here in detail. That is why I do all my intensive tests.That is why I am explaining photographers should not uncritically rely on manufacturer's datasheets only.
Suggestion:
I have always showed my results life to other photographers at meetings. Of course I will be at next Photokina again (and at the analog-days, see below). If you like just join and we can talk looking in real life at the negs, slides and prints.
The discussion here is at a dead end.
Looking through a magnifier yesterday, it would take an 8x10 sheet of Ektar film to be printed 14 feet wide just to begin to detect grain with a decent pair of reading glasses right in front of the print. But even on my early Cibachromes printed to 30x40 inch size from 4x5 old Ektachrome 64 film - distinctly more grainy than today's equivalents - one has difficulty detecting the grain even right up to the print, and that's a very contrasty, high-acutance medium!
No one here is disputing that. I know how very fine grained film can be. I've more than 12,000 test shots in my archive here, and the number is increasing year-by-year.
But I even don't need my archive for proving that, looking at my prints is often enough evidence for it

.
And projecting my slides: Even 35mm Provia 400X pushed one stop has no visible grain on my screen with 1.5 meters width at normal viewing distance. I have to put my "nose on the projection screen" to see the grain (and even then it's very fine). And with the Velvias, Provia 100F, Astia, Sensia, E100G, new E100 etc. grain is even much, much finer. So fine that you can project 35mm slides as big as you want.
There is a reason why for decades professional 35mm slide (Audiovision) shows on huge screens (cinema size) have been state-of-the art with their unsurpassed picture quality. The audience has always been enthusiastic by the brillance, wonderful colour and outstanding detail rendition of these 35mm slide shows.
One of the most famous camera manufactueres will make a big event called "Analog-Days" this year. They plan for thousands of visitors. They have asked me to offer lectures and workshops there. And what I am really looking forward at that event will be slide Audiovision shows by one of the best nature and wildlife photographer worldwide (the official announcement will be out in about a month).
Best regards,
Henning