First a brief introduction: I am a regular reader of LuLa, but not of the forums, so please forgive me if I'm saying anything stupidly obvious or that has already been hashed over a lot. I claim no photographic expertise, but I have recently been strongly considering upgrading to medium format, so read the "Everything Matters" essay with interest.
I have two quick comments about the essay. First is that I was reading along happily (I feel I can relate to his comments on "hyperreality", while I agree with others that it's only one possible style of photography) until I got to the image comparison, and was shocked at how bad the medium format image looked. I tried looking at it on two different computers and couldn't figure out what was going on, which drove me over here to the forums, where I eventually discovered that the problem was that my browser (Chrome) wasn't rendering the colorspace properly. If I would change one thing about the essay, I would have the jpeg redone in a colorspace which doesn't have this issue, or put a huge disclaimer that if it looks wrong, you should change browsers (actually, such a disclaimer might be helpful more generally -- I went back and subsequently looked at other images elsewhere on the site in different browsers and found they were also suffering from the issue, and I had never known it!)
Secondly, I was disturbed to find that the "smaller format camera" was apparently an iPhone. I do find the wording describing the comparison to be deeply misleading, if not outright false (as per the discussion of RAW), and would urge that the wording be clarified in the name of transparency. I don't see how being coy about the iPhone adds anything to the article other than the feeling that the author is trying to pull one over on his readers.
Anyhow, the main issue I wanted to discuss is my point of view on all the discussion of scientific (or less scientific) testing of how different cameras compare under different circumstances. Even before the present article, I was struck by the contrast between MR's article "You've Got To Be Kidding" and comments he has made in other articles to the effect that medium format seems to be recognizable even on screen (eg in the P65+ field review). I'd love to see this apparent conflict hashed out (particularly before I shell out for medium format!), ideally with more of the sort of tests carried out in the "Kidding" piece. One possibility that jumps out to me from the sample images in "Kidding" is that the scenes themselves appear to have relatively low dynamic range, and relatively low fine detail, so this may explain to some extent the contrasting experience.
Two key questions I'm curious about are: to what extent is higher resolution actually visible on smallish prints, and what is the actual comparison between dynamic ranges? These could both presumably be tested by taking good test images (i.e., with very highly detailed scenes, and large dynamic ranges) with good MFDBs and high-end DSLRs, processing and printing with normal workflow (supervised by people on "both sides", if one really wanted to be fastidious), and then having subjects (chosen to have good credentials, as in the "Kidding" article) look at the prints without being told what they're supposed to be looking for. I'd be extremely interested to read about the results of such tests (I understand that tests of this general sort have been carried out on the resolution question, and indicate that resolutions well above 300dpi give perceptible differences, but it seems there's still some controversy about this?).
I am interested to hear about the scientific/engineering reasons why something should or should not be perceptibly different/better than something else, but I always take such arguments with a grain of salt. I am scientifically oriented by nature, but it's also easy to get carried away by coming up with particularly measurements and theories and stacking a bunch of them together to make a conclusion. Although this will have a veneer of scientific authority, in my opinion it is much more scientific to actually carry out a well-controlled experiment, as for instance described above. Emil Martin's forum piece trying to combine DxO's various measurements to extract a photographic dynamic range number looks like a first-rate example of the first approach, and far better than nothing, but in my opinion would be definitively trumped by a carefully controlled print comparison showing contrary results. I feel that there's a huge discrepancy between claims of roughly comparable DR versus a six-stop difference, and I can't imagine it would be hard to figure out which is right by testing. I am naturally skeptical, but of both approaches: I appreciate how knowing what you're looking at can bias your perception on the one hand, but on the other hand feel there's plenty of history where scientists/engineers think they've worked out all the relevant measurements, only to discover later they were missing some crucial aspect of the situation.
One last comment: in some sense, only positive results of controlled tests as above are definitive. A negative result only says that the people being asked to look couldn't tell the difference between the particular cameras used for the particular scenes used. Such tests can never prove that two sensors are always equivalent for a given print size. However, if a given test is trending towards negative, the obvious thing to do would be to run it again, but with someone who feels strongly that they see such differences (such as MD) as the viewing subject (and not, obviously, involved in preparing the prints). I've experienced firsthand that different people have differently discerning perception (probably based largely on experience and training), so it's a valid objection that a negative test might not have involved the "right people". But at the same time, from my point of view it's also worthwhile to know which differences are or are not readily apparent to the average educated viewer. So I feel like any such tests will be interesting.
OK, hope that wasn't too long-winded.