Quoted:
Rumor is out today that it will be officially announced next week, it looks like canon is trying to play the pixel game and catch up with nikon
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Sony sensor so this should more than catch up to Nikon's D810, and catch up to it's dynamic range. To give you an idea on how old the 5dmk3 sensor is, the D700 (with the D3 sensor) has the same or slightly more dynamic range, iirc.
It will be interesting once Canon announces all three... 5ds, 5dsr, and the 5dmk4. The rumor specs tend to suggest the 5dmk4 will not have a competitive Nikon until they come out with the true D700 replacement with D4 internals.
This is a shot directly across Nikon's bow is how I see it. I see excitement with the 5dmk4, but once everyone gets past the megapixel hype of the D810, 5Ds, and 5Ds R, they'll realize lenses to resolve to those levels will make the body look cheap, cost-wise.