keep your self to the subject and look at the specs
Ok. When I look at the 5DIII vs. the D800, I see a faster frame rate, better AF, better ergonomics and UI, much better Live View, and compatibility with better lenses (including those from Nikon, if one is willing to control them manually). Oh, and a bit less DR. Therefore, overall I see a better camera
in the 5DIII. But then again, when I look at the specs, I'm not DRunk on DR and wearing DxOMark blinDRs.