Some more reflections:
The microscope images are very informative. On the IQ-180 then lens clearly has a lot of MTF at Nyquist, so we get aliasing instead of resolution smoothly going away with increasing frequency.
Without doubt, the 8x10" outresolves the rest.
If we compare the 4x5" there are some advantages and disadvantages to 4x5" compared to P45. The P45 obviously has different artifacts, regarding resolution it may sometimes resolve detail the 4x5" does not, check the hose in the right part of the image.
In my view the Alpha 900 holds up well in the enclosed image.
I may need to point out that I have tested my Alpha 900 against both Velvia and Ektar 100 on my Pentax 67. In my test it was quite even, but the A900 image was much easier to work with. For that reason I find it interesting to compare with your test. I also guess that the Mamiya has a much better lens than the one I had on my Pentax a 90/2.8. So I have a significant interest comparing your findings with mine.
My tests are here: http://echophoto.dnsalias.net/ekr/index.php/photoarticles/59-sony-alpha-900-vs-67-analogue-round-2http://echophoto.dnsalias.net/ekr/index.php/photoarticles/16-pentax67velvia-vs-sony-alpha-900
Seeing your results, it's fairly obvious that the best films give better and more detail on 4x5" compared to P45 and quite clearly the 8x10" beats IQ180 for quality.
Very obviously, when you compare the smaller sensors (135 FF) to large format the images fall apart. I'd say that your tests also show that there is a lot of difference between different films.
Most of my testing was done using a Minolta Dimage Scan Multi Pro, which I believe is a decent CCD scanner, but my film images may have been handicapped by the scanner. One other point is affordability. With analogue the equipment is quite affordable especially if we can find used equipment. High end digital tends to be very expensive.
Thanks Erik, really appreciate the support - the comparisons between the different cameras are subjective but I thought it would help to show a side by side directly between the cameras you mention..
Personally I read the results differently but that's the good thing about a simple side by side. The results can be interpreted by the reader.
p.s. The reduction in resolution of the 8x10 in the field is, I think, more to do with diffraction than wind - otherwise specular highlights would have been smeared - only conjecture though.