Thanks. Would you kindly be able to do the same PDF exercise with my PDF client of choice, which you can get free from the App Store:
https://pdfviewer.io/store-ios
This would imply that there is little change between 6GB and 8GB when it comes to rendering heavy PDF files. It would be ideal if someone with a 1TB+ model on 16GB could run a similar test to see what happens then, but it does appear to me that one good justification for a 16GB model is such a use case. It is clear that large PDF files task the RAM far more than video rendering programmes or similar.
Incidentally, my A12Z CPU is little more than idle during the rendering of heavy PDFs, and does not appear to be the bottleneck at all.