From all the reviews I see comparing it with other cameras, the Canon 5d mark III seems to blow everything else away except in dynamic range and shadow noise. The 5D3 does look fairly bad when the shadows are pushed while the Nikon D600 & D800 are clean. This is a huge asset as being able to boost the shadows would bring back a ton of detail in landscape shots. Check out the comparisons: That's true but depending on what your priorities are, it's also an asset to have great AF and high ISO.
5D MKIII w grip, 70-200 2.8L IS II, 24-70 2.8L II, 16-35 2.8L II, 100 2.8L IS macro, 600EX-RT