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Comparing the top of the line MF back with the top of the line DSLR
The images below are used by the kind permission of Tim Ashley, who published them on getDPI in this article.
The images can be downloaded here, please only download if you are really interested, we don't want to blow Tim Ashley's drobox limit!
The first image is actual pixels view of shadow detail from both IQ180 (top) and D800 bottom. In my view it is pretty clear that the IQ180 is a bit more noisy.

Findings
The IQ180 image has noisier shadows compared with the Nikon D800E image. The difference is visible in both actual pixels view and with the IQ180 image downscaled to D800E image dimensions.
It is possible that better results would been achieved by Capture One, but I'm pretty sure the comparison is pretty relevant regarding raw image data.