I'm struggling with this decision as well. I didn't upgrade to the 5D3, and the 1D series just doesn't apply to what I shoot. I'm almost entirely landscape, a little macro work. Very seldom do I even use autofocus, of course when you do you want it to perform.
I "think" either one would be a significant upgrade in all areas from my 5D2. Love the resolution of the 5DSr, love the dynamic range of the 5D4. Either should be better on noise with the advantage going to the 5D4.
Hard decision, I nearly bought the 5DS when they came out, but decided to wait for the 5D4 to see what it had. Really it hits all my marks. I suppose the only thing I get with the 5DS is the higher resolution.



