Well, I guess I'm just a numbers kind of guy, so I took all six files into PS for a look. Noted that they were all sRGB except the DPP file which was Adobe1998. Converted it to sRGB before making comparisons. The histograms are interesting; in RGB the green and blue channels are quite similar in shape for all six files - the big differences are in luminosity level; the red channel shows significant differences in shape between files, in addition to luminosity differences. The differences in luminosity confound visual attempts at hue discrimination. I took the files into LAB for some measurements. The model's eyes, and hair, are nearly identical in color across all six files - perceived differences are due primarily to luminosity (contrast and level) differences. The greatest difference is in the rendering of the lips. Measuring the same location on the lips in all files, all but C1 have the same level of yellow (C1 is higher than the rest). Silkypix is the most magenta, DPP the least. Measuring the same location on the cheek in all files, all have roughly the same level of yellow. RSP is the most magenta, DPP the least. Rank ordering the converters for magenta level from greatest to least: for the lips - Silkypix, Bibble, RSP, C1, ACR, DPP; for the cheek - RSP, Silkypix, ACR, C1, Bibble, DPP. The luminosity levels of the files could be brought into alignment with a tonal curve adjustment. Color is more problematic, they can be brought closer (an infusion of magenta to DPP for instance), but I doubt an exact match could be attained. I would be interested in knowing which lip shade is most accurate. I'll bet the model could tell us (with a degree of accuracy exceeding the most sensitive colorimeter), or I don't know women!
Dave