Today I had an opportunity to participate on local Canon 5DS(R) presentation, play with production versions of both cameras and quickly compare to my 1Ds mark III.
I refused to do any outdoor comparisons and focused just on the studio shots (as there is lot of outdoor samples and RAW files in the wild already and the time was limited).
I've used Canon EF 2.8/100L Macro and Carl Zeiss Planar 1.4/85 ZE on all cameras. Files are processed in latest version of Capture One 8 (8.3.0.83). As the production RAW files probably slightly differ from preproduction samples, I refused to use included 5DS(R) profiles for C1 and used 1DsIII color profile with custom WB and adjusted all files to look as close as possible.
Default sharpening, chroma noise reduction down to 0, luminance 0, detail 100. Except adjusting WB and exposure to match on all images, no other adjustment was done.
As bonus, 5DS(R) JPEGs processed with latest DPP4 are included. I really do like the Fine Detail picture style and I hope, that my 1DsIII will be soon supported too in DPP4. DPP4 shows definitely better the differences in skin tones rendering between Canon and Zeiss lenses. I've applied DLO on EF 2.8/100L shots, to extract as much details as possible.
As there is currently not possible to process 1DsIII and 5DS(R) files in same version of Canon DPP, I processed the Planar shots with DPP3 and DPP4 with Standard picture style to compare the color rendering with Canon software.
Because the fullres 5DS(R) JPEGs are too big for my image hosting site, I offer only download of zipped full size JPEGs (~185MB).
http://www.mediafire.com/download/h47zsru133878xh/1DsIII_5DS_5DSR_Studio_Comparison_JPEG.zip
Because nobody cares about some other person JPEGs :
, you can download RAW files too and play with them (~246MB, C1 and DPP4 settings included) 
http://www.mediafire.com/download/q2a5f7qgnsb51su/1DsIII_5DS_5DSR_Studio_Comparison_RAW.zip
If you want to process the 5DS(R) files with DPP4, you need to download latest version 4.2.32.0, because the previous version 4.2.31.0 doesn't work with production RAWs.
File names are self explanatory and full EXIFs are included.
I do like the 5DS(R) output, it's very close to what I'm used to (1DsIII) and the resolution bump is significant. Unfortunately, I don't print bigger than A3, so I don't see a reason to upgrade anytime soon....
I refused to do any outdoor comparisons and focused just on the studio shots (as there is lot of outdoor samples and RAW files in the wild already and the time was limited).
I've used Canon EF 2.8/100L Macro and Carl Zeiss Planar 1.4/85 ZE on all cameras. Files are processed in latest version of Capture One 8 (8.3.0.83). As the production RAW files probably slightly differ from preproduction samples, I refused to use included 5DS(R) profiles for C1 and used 1DsIII color profile with custom WB and adjusted all files to look as close as possible.
Default sharpening, chroma noise reduction down to 0, luminance 0, detail 100. Except adjusting WB and exposure to match on all images, no other adjustment was done.
As bonus, 5DS(R) JPEGs processed with latest DPP4 are included. I really do like the Fine Detail picture style and I hope, that my 1DsIII will be soon supported too in DPP4. DPP4 shows definitely better the differences in skin tones rendering between Canon and Zeiss lenses. I've applied DLO on EF 2.8/100L shots, to extract as much details as possible.
As there is currently not possible to process 1DsIII and 5DS(R) files in same version of Canon DPP, I processed the Planar shots with DPP3 and DPP4 with Standard picture style to compare the color rendering with Canon software.

Because the fullres 5DS(R) JPEGs are too big for my image hosting site, I offer only download of zipped full size JPEGs (~185MB).
http://www.mediafire.com/download/h47zsru133878xh/1DsIII_5DS_5DSR_Studio_Comparison_JPEG.zip
Because nobody cares about some other person JPEGs :


http://www.mediafire.com/download/q2a5f7qgnsb51su/1DsIII_5DS_5DSR_Studio_Comparison_RAW.zip
If you want to process the 5DS(R) files with DPP4, you need to download latest version 4.2.32.0, because the previous version 4.2.31.0 doesn't work with production RAWs.
File names are self explanatory and full EXIFs are included.
I do like the 5DS(R) output, it's very close to what I'm used to (1DsIII) and the resolution bump is significant. Unfortunately, I don't print bigger than A3, so I don't see a reason to upgrade anytime soon....