Unbiased test: everything the same. Comments:
Shutter speed doesn't matter unless there is motion. With motion there will some unsharpness.
Lens: Almost any lens is best at f/8 so f/8 or best aperture should be used. Preferably an excellent lens.
Lighting: The important is that is the same for all lenses. To illustrate tonal range and DR it should be contrasty.
Subject: Should be the same. Some type of synthetic subject is best.
DPreview and Imaging Resource have good synthetic test targets. AFAIK the only MF system they have tested was the Pentax 645D.
OK, I know there are other factors like camera vibration, from mirror and shutter, leaf shutter that can sync at 1/800 etc.
DR can probably illustrated best by publishing a raw exposure of a Stouffer wedge.
Here is what I made of the Pentax 645D test at Imaging Resourse: http://echophoto.dnsalias.net/ekr/index.php/photoarticles/51-a-closer-look-at-pentax-645d-image-quality
So we've got one variable covered...
What about shutter speed? iso? Lens? Lighting? Scene/ subject?
The naysayers (from both sides) will always dismiss such a test for one reason or another. Hence why I do MY own tests and always encourage others to do THEIR own...