So, in sum we have this
These tests provide at best, a quick glance of the cameras overall available IQ within the tests boundaries. But, we can't stop there. Glass and the cameras CPU and firmware are also factors that play a roll is the final IQ. Yes, this test involves these too. But the data pulled are a few areas that photographers what to know, or are lead to believe that "This" data is what you decide on to make a buying decision.
I liked the analogy of the film to finished print, and all the steps involved to get there...IF ONE area is lacking in Quality Output, than the final result suffers too.
I'd venture out on a limb here and say that the TOTAL output of a M9 is marginal to most of us. And, a few can tell the difference in IQ because of their higher scrutiny of the different areas of a file..IE: for example: DR 11.0 vs DR 11.9...Maybe 3/4 stop, but, At that level..How fine is tonal separation to be distinguishable by the human eye?
As may have said, it is the final result that counts in the long run.
I believe, as others, that because there is plenty of great fast glass out there, that HIGH ISO IQ is not the biggest selling point, but excellent glass is., so as to use lower ISO. BUT... I have seen some great ISO 2500 M9 images...so maybe the test is relevant on some levels, but not to most photographers who produce images of interest, not, just test images.
High speed glass, can help you gain 3 stops (like f/2.8 to f/1.2 or f/1.1). But, think about. If you are shooting at f/1.4 or faster, your DSLR may not be able to AF, and MF is a drag w/o a RF/Split doughnut and even then, it is may still be darker than a RF VF. The High end DSLRs might be able to, but, just buy an M9 and 2 fast lenses. Like a 50mm f/1.1 Nokton, and a 24mm f/1.4 Leitz, and spend 11k? You'd spend 6k on a D3x and then the Nikkor glass. And spend close the same. The M9 with those 2 lenses are a lot lighter to carry around too.
So, it may boil down to weight and Faster MF'ing. and, knowing the IQ will be there.
Or, just being able to use all that Leica, Canon SM, Nikkor SM and Voigtlander glass you have accumulated over the years.