with interest I read your test comparing a lot of things with obvious results.
For conditions in a photographic studio the test seems OK for me.
I miss a comment pointing out, that these conditions might not to be transferable to outdoor photography, specially with 400, 800 ASA, as people photography with medium format cameras uses to be done due to the optical construction of this kind of equipment compared with 35mm-based cameras.
I wonder how things change comparing the image quality of digital backs higher than 160 ASA to the digital image quality of digital-35mm reflex cameras and high quality scanned c-41 film (120 and 4/5 inch) at 400 ASA.
Another important point for the overall quality of digital images is imho the character of dynamic range and highlightclipping of digital or film above 100 ASA.
I guess if under these additional conditions you will have a quite different overall result of your tests?