Forgot to add this link in there, which is pretty crucial when considering going to the 5DS line..... AND soon the 5D4. It is a list of all the compatible lenses for the 5DS line and don't quote me on it, but this list will be nearly identical for the 5D4. One lens that isn't included which i and many other shooters believe to be optimal is the 35mm 1.4L.
http://www.the-digital-picture.com/N...spx?News=15356
LENSES ARE EVERYTHING.