I'm really surprised at how much I see the 5DS/5DSR that is negative (and in my experience actually using them, often times completely wrong), usually written by people who have never used one.
I had two 6Ds, two 5D IIIs, and a 7D II, and also a 1DX. I sold my two 6Ds when I bought my 5DSR. After shooting a concert from soundboard, using the 7D II, 5D IIIs, 1DX, and 5DSR, swapping lenses around to compare apples to apples, I sold the 7D II - the 7D II image quality was just strikingly lower in comparison, and the "reach" advantage evaporated.
The ability to crop on this camera is stunning - I can take a shot of a drummer from soundboard and crop down to the end of his microphone and have details of the grill on the end.
Using it a lot since launch, I just sold my two 5D IIIs to get a second 5DSR.
I hate the term "game changer", but that is what it is for me. I am NOT a studio photographer.
The files from the 5DSR just look SOOOOO much better. Even going through my shots in Lightroom, I can immediately identify (without zooming) which shots were with the 5DSR and which were with my other (lower res) bodies. They are just so much richer, and I like the color better too.
I do mostly action photography, oftentimes in challenging light, sometimes from a distance, and almost always handheld, and I've not had any of the problems that others seem to speculate about who have never used a 5DS/R.
To me, it's essentially a 5D Mark III with more than double the resolution and better quality images.
My only problem was just having one 5DSR body. Since I am often time constrained, I like to have multiple bodies to be ready with different lenses, so it was hard for me to decide which lens to pair with the 5DSR. So essentially trading in two 5D IIIs for one additional 5DSR I guess says a lot about how I feel about the camera.
I love it with the 300mm f/2.8 II and the 100mm L macro the best.
Canon 5D Mark III (X2) | Canon 6D (X2) | Canon EOS M | Canon 16-35mm 2.8 II | Canon 24-70mm 2.8L II | Canon 70-200mm 2.8L IS II | Sigma 35mm 1.4 | Canon 50mm 1.2 | Canon 85mm 1.2 | Canon 85mm 1.4 | Canon 135mm f/2 | Canon 300mm f/4 | EF 40mm f/2.8 STM | Extender 2x III | Extender 1.4 III