There's like a mile of gap between my 5D and my older P20 (non plus) and that's even when I use the brilliant Leica R lenses on my canon. There's several stops of usable DR more on my p20 than the 5D. If the 5D 2 got 1 stop more DR than the 5D classic then it still wouldn't match up to my 5 year old P20. I am a big doubter that the 5D2 or D3X are going to replace even 2 or 3 generation older MFDB's for studio use. I think Michael wrote in the first DXO/MFDB thread why the DSLR numbers come out so favorable for DR - something about in camera noise reduction while MFDB's rely on on RAW processing software. The DXO numbers for at least DR are not useful for comparing DSLR to MFDB.
It is interesting to note that the people who claim that MFDBs are "better" generally talk about what they see, and what their customers see, i.e. a clear visual superiority for the MFDBs. The people who claim that the difference is very small are generally talking about statistics, plots, measured noise, and so on. There are a small number of people who go against the stream and claim that they can see no difference, or measure no difference.
This leads me to wonder about two things:
1) Could they both be true? In other words, could it be that the MFDBs give visually noticeably more appealing results, while there is little measurable difference? That would mean that what we measure doesn't translate directly to what we feel about the results. This would lead me to think that if we want to measure how good something is, we need to come up with new tests and new ways of measuring. Especially the DR results make me think this. One hears repeatedly how much cleaner the shadows are with MFDBs, but this somehow doesn't translate into better DR results, counter-intuitively, I suppose because what we like and what we can measure don't match.
2) Could it be that the 35mm-FF camera manufacturers know about the lack of significant measurable differences, and are actively pushing this angle by "cooking" the results to obtain the best possible *measured* result? They must surely know that very few people will ever see top-notch MFDB results, and that cooking the results to minimize the measurable differences helps them sell more cameras. This is somewhat analogous to graphics card manufacturers writing drivers which are specifically optimised for certain gaming performance benchmarks, while performing no better than other cards in actual play...