Actually, that looks like a pretty big difference to me, considering the 1DsmkII is only expected to have 14% more linear resolution.
It is a big difference, but it's a big difference on a huge print that would be far larger than any giclee type printer could handle.
On my 19" monitor with screen resolution of 1280x1024, a 400% enlargement of the entire image equates to a print size of approximately 17.5 feet wide. If I view such a print from a distance equal to the print's diagonal, then such differences that I see viewing the 400% crop from a distance equal to my monitor's diagonal, disappear completely. In fact, I only have to step back about 12ft from my monitor for those differences to become undiscernible.
Now I know people have a habit of walking up close to a print, whatever the size. I some times do this with billboards to check out the size of the ink dots (just out of curiosity ), but I submit, if these two 17.5ft wide prints were side by side on a gallery wall and you wanted to compare micro detail, by the time you'd walked over to the other print, you'd probably have forgotten the precise nature of the micro detail you'd been examining just 30 seconds ago. (Maybe not ).
I haven't made any prints of these crops yet, as Tim suggests, but at 67% enlargement on my monitor, the full size image is as big as my Epson 7600 can handle without borders on all 4 sides (ie, 36x24").
At this degree of enlargement (67%) the differences clearly visible at 400% are no longer discernible. It's my experience that what I can't see on the monitor, I can't see on the print (excluding subtle hues of color that might be outside the gamut of the monitor but inside the gamut of the ink and paper).
By the way, that 14% increase in resolution that the 1Ds2 is supposed to have is a theoretical calculation that can only be realised with a perfect lens. It represents an increase in sensor resolution as opposed to system resolution. In practice, the resolution increase will always be smaller and herein lies the difficulty as I see it.
The 30% increase in pixel count, of the 1Ds2, appears fairly substantial and creates the impression that the resolution increase should be substantial. However, the resolution increase in terms of lp/mm along one dimension is a theoretical maximum of 14% and probably no more than half that in practice.
In my view, some people incorrectly interpret this small increase (say 7% in practice) as an indication that current lenses are simply not good enough to justify any further increase in pixel density. My interpretation is, a 30% increase in pixel count is simply too trivial to make a worthwhile difference. You need to double pixel count to get an improvement that hits you in the eye. Such improvement, however, would be overkill for the printing of uncropped images at normal or average print sizes, but great for those wanting to get the most from their longest lenses, or for those occasions when an interesting composition can be found by heavily cropping an image.