The 5DS/5DSR is an extended version of the 5DIII (or a competitor specifically launched for Nikon cameras of the same class) whose operation, housing, processor, etc. are no different from the 5DIII. The difference: 5DS is a high pixel version of 5DIII (seems to have reached the ordinary medium format pixels) 5DSR is based on the 5DS without the “low-pass filter” (low-pass filter is a device used to eliminate (reduce) moire in front of the sensor).
Both performance is basically the same, are 50.6 million high pixel full-frame SLR, for the pursuit of SLR photography pixels, image quality and fineness of the photographers of these two machines is the king. Only the 5DS is equipped with a low-pass filter on the sensor. The 5DS with a standard low-pass filter addresses moire and artifacts; the EOS 5DS R offers better sharpness, but photographers must consider moire and artifacts. Although post-production can solve the problem of moire and artifacts, it involves a complicated process, and if it is a film shoot, the situation is even more complicated! If asked to choose between the 5DS and the 5DS R, I would say that if you are a meticulous landscape photographer, looking for the ultimate in resolution, and have the patience and skill to do fine post for every photo that shows moire, then you should go with the EOS 5DS R. But if you want a high megapixel camera that does it all, then you should definitely go with the EOS 5DS! There is no moire problem, most of the cases are sharp enough, and the price is a little cheaper, so why not! After all, 50 megapixels is already very impressive ……
If the studio, and need to correspond to the high pixel large format output printing, you can consider the 5DS/5DSR (the money is completely spent on high pixels).