In this conversion I have used Imatest internal conversion, based on DCRaw. I can get much better results using LR4, for instance.
The first test I have done was with the 24-70/2.8 ZA lens but the second one was made with the Macro 100/2.8. The Macro 100/2.8 gave much better results which may depend on less internal flare.
The DR you can get trough a lens depends much the size of the brightest patch. According Norman Koren's test most good lenses have about 0.5% flare (or so), that would limit DR to about 8 stops. If the bright patch is small it would be possible to have a much higher DR.
In practice I can see a DR of about 9-10 EV in my raw data, using RawDigger. I have found some files with wider DR but those typically included the sun (like setting sun).
Of the about 65000 images I have on my computer I guess that a few dozens are limited by DR. I have just found a couple of images that really got better by multiple exposure HDR, but in many cases some significant tone mapping effort has been necessary to make a good image.http://echophoto.dnsalias.net/ekr/index.php/photoarticles/61-hdr-tone-mapping-on-ordinary-image
Your imatest numbers are definitely less than mine for testing similar backs (p20, CF 22, CF 528, CF 39, etc) however I can't say why yours are lower and I haven't run your files through imatest myself. In my own testing, the imatest low values come closer to DXO's values and also fit with the sensor manufacturers stated DR. But does DXO test camera and lenses or just the sensor? Lenses may limit contrast and therefore DR - so they may have some effect. In fact as a side discussion, I wonder what the DR limits of lenses are? I've read somewhere that the most we can expect through good real life lenses is about 13-14 stops. Anyone have any info on that? Certainly we are at the point where the lenses can make the difference.
Since I have tested many cameras, the thing I find most useful is the ratio of drop from low to high values in imatest. DSLR's of past used to drop quite a lot from low to high - ie about 4-5 stops. Current generation DSLR's like the Nikon d800 don't drop as much between the ratios. I find the Imatest High value of most use to evaluate how an image will hold up through the editing process.