Remember, diffraction limits are very real. I deal with them almost daily with my very dense pixel 7D. My 500mm is excellent, but I generally limit myself to f/8 to minimize visible diffraction. At f/16 it can easily be seen.
So, if you like to shoot landscapes with DOF from the front of your tripod to infiinity and routinely shoot at f/16 or even f/22, forget about it with the D800. The diffraction will ruin all the sharpness that you used to get from tripod, mirror lock up, remote release and small aperture. F/11 is about as small as you'll want to go and, preferably f/8. The 22MP Canon 5D MkIII will be a much better landscape body.
See and calculate visible diffraction limits for various cameras at:
Diffraction is physics that can't be overcome with a better lens or better processor churning the sensor's information. A true sharpening program, not Unsharp Masking, could probably improve detail, but it's simpler to understand how pixel size relates to detail resolution potential and select your sensor accordingly.
Put a big ole 600mm super-tele on the D800 and shoot a bird wide open and the feather detail will rock you back in your seat, but try to put a 17mm on it stopped down to f/16 and you'll prefer the D700 every time.
Sorry to be the bearer of bad tidings for some, but there's no free lunch when it comes to optics and physics.
One camera cannot do everything equally well, so you need to pick based on your needs or carry two cameras, like I do.