Measuring the DR has nothing to do with ISO. The ISO is relevant only so far as higher ISO reduces the DR. However, if the question is the maximum DR, for example for a landscape, then it does not matter which camera at which ISO has the highest DR; the only thing matters is, how high that DR is.
Panopeeper, Eric is not referring to the camera's sensor gain ISO control, he's referring to the International Standards Organization standard on noise measurements in photography/electronic still-picture imaging, or ISO standard 15739:2003
. This standard does contain a definition for dynamic range (in addition to definition and measurements of noise) for digital still cameras.
And Eric is correct--the standard's definition for dynamic range for digital still cameras has signficant flaws. In fact, I just googled the standard and found an excellent paper on both the standard, and its flaws relative to digital still cameras. You can read it at: http://doug.kerr.home.att.net/pumpkin/ISO_Dynamic_range.pdf
. Doug does a superb job covering this, so I'll leave it at that.
Egill, in the end, I'll second both Juanito's and Eric's advice (third their advice?). The specs are only meaningful if you have a lot more information than Phase is providing. As Eric suggested, test with a transmissive wedge or even a contrasty scene (much easier) and trust your eyes.
Remember, by the time you see an image from your raw file, the image may have gone through any number of gamma conversions, level adjustment and subjective (by your raw developer manufacturer) tweaks. Reconstructing the imaging chain to get back to the raw data is not trivial, if you want to understand how the raw data maps to real-world quality of your images.
Just doing a side-by-side will save you more than a little time, and tell you what you really want to know, particularly if you begin lifting the shadows and looking for artifacts, again as Eric suggests.
Hope that helps,