When shot side by side, the OOC images out of the DP2Q and DP2M can look quite different because of differences in the respective camera's choice of default exposure, contrast, sharpness settings and differences in white balance (DP2M is colder with more magenta cast while DP2Q is warmer and more natural). Then during RAW processing with SPP, SPP 6 applies more noise reduction to DP2Q RAW files while none to DP2M RAW files.
With post-processing to equalise the image quality settings between the Quattro and Merrill images, they would approach each other in image quality. Also, users have found that with different SPP settings, the Quattro images would look more like the Merrill ones except that the higher resolution could actually translate into more details in the Quattro images.
http://www.dpreview.com/forums/post/53955459
http://maros-notebook.txt-nifty.com/notebook/2014/07/sigma-dp2-quatt.html
The dilemma here is for users who do not want to do any post processing at all or prefer to shoot JPEG only. Then the differences between the Quattro and Merrill images would be quite visually significant.