Thank you Anders,
These tests seem to confirm and somewhat quantify several predictions about sensor performance comparisons, in particular the advantage in moderate shadows of a larger sensor due the fundamental advantage of being able to gather more photons and thus diminish the effect of shot noise, even while the smaller sensor with less dark noise has an advantage in deep enough shadows and when the sensors are severely "underexposed" (meaning, used at an exposure index well above their ISO base sensitivity).
One suggestion: for sensors like the MF CCDs and Sony/Nikon CMOS, the noise seems to enternthe signal almost entirely before any gain is applied, so that the DXO measures of SNR on an 18% gray card at various exposur index settings can be reinterpreted as measuring the SNR in darker parts of the image, at least as a rough guide. For example, the ”midtone SNR" given there at exposure index 1600 is probably a good estimate of SNR in a shadow region three stops below the midtones at EI 200.
But beware: the DXO calibration of "ISO speed" is complete nonsense when applied to those MF CCDs, so it is better to look at the manufacturer's stated speed ratings. The problem is that when a DMF back takes advantage of its 16-bit ADC to position the midtones further down from maximum signal (while still having them at roughly comparable numerical levels, but with the maximum numerical level being four times higher than with 14-bit output), DXO absurdly calls this a two-stop over-statement of ISO sensitivity. This is due to DXO confounding a definition of base ISO speed relative to saturation of electron wells at photosites with "saturation" of the levels in ADC output. The bottom line is that the DXO curves for DMF backs should effectively be pushed about two stops to the right before making comparisons to smaller format sensors.
This DXO quirk has far smaller effects between other DSLRs, which generally do not have the same great surfeit of ADC levels relative to the dynamic range of the signal being digitized, and so tend to position the midtones at roughly the same fraction of maximum ADC output level rather than leaving an abundance of headroom.
