The main areas where the 5DSR can perform really well are colours, sharpness and detail. In controlled environments where you shoot at the lowest ISO, you can achieve some of the absolute best image quality. The colours tend to be more vibrant and accurate based on my testing and the detail is significantly more.
Personally, I much prefer the 5DSR, the incredible image quality and detail are very appealing to me. Most of my professional shoots are done using manual lenses, therefore I tend to take my time for each image ensuring I'm getting the best results. I enjoy shooting with more layers and bringing out the extra detail in post, that to me is part of the fun and not at all a chore.
Before doing this comparison I didn't enjoy using the Mark IV very much at all because to me, it represents a little bit of a middle finger from Canon. Having said that, after doing all of these tests and comparing it to the 5DSR, I now firmly believe that it is one of the best cameras you can buy. For most people, the Mark IV is a much better option, the 5DSR is far too niche of a camera for the majority. Yes, the 5DSR does have better image quality, however, image quality is not really that important when comparing cameras at this level. For that extra detail and resolution, you will be sacrificing far too many useful features to make it worth while. On top of that, the Mark IV will dramatically improve your workflow when compared to the 5DSR. The cleaner and more flexible images straight out of the camera from the Mark IV mean that for most uses it is far more effective.
I'm still quite disappointed in Canon for releasing a camera with such unnecessary and obvious limits. Even with that, however, I strongly recommend the 5D Mark IV above the 5DSR.