There are a few points I would like to add to the discussion here:
1. ISO has always been one of the main factor when folks speak regarding to digital sensor or DSLR. The higher ISO of DSLR may have lower signal/noise ratio compare to the MFDB or from one DSLR brand versus another brand such as Nikon versus Canon. However, often enough no one will speak about the higher ISO colors and texture. I find that I like the rich colors and the texture (less plastic) of the MFDB at high ISO much better than I would like the Canon file; even the higher ISO of the Leica M8 looks nicer than the Canon file IMHO. The Phase One P+ series backs are extremely good at high ISO. Folks claimed that the ISO 800 is very nice and I concurred to their claims but in addition, I find the ISO 1600 on the P30+ to be very good as well. Here is an example of the P30+/Contax 645 + Hasselbald Planar T* 2.0/110 FE at F2.0 handheld at night with no flash and processed with Capture One default setting and no sharpening applied (see image). In addition, ISO noise may be attenuted significantly if the exposure is properly set.http://i189.photobucket.com/albums/z265/Ad...07ISO1600F2.jpg
2. Dynamic range (already spoken) especially with the new improvement from the Phase One P+ series (leaving the mechanism out here) and gain may be important in certain applications and post processing.
3. Optics is an essential topics and one must identify the lens that works best for one's own application. Like DSLR and MFDB comparison, the optics for 35 mm versus the medium format system is also different in terms of depth of field, bokeh, resolution, and spatial compression. IMHO I prefer the medium format image circle more due to the characteristics of the above mentioned. Furthermore, different brand within the same image circle optics offers different characteristics.
4. Speed is also important for certain application but we see now the Phase One P+ series and Leaf Aptus S series are becoming more than adequate to do fashion works.