Well, as expected on 100% comparison 5dIII blows D800 out of the water. It's a t least 1 stop better, but we must not forget that scaled down images just might look pretty much the same, as the D800 has so much detail captured.
Wondering how do they compare scaled down???
What I'm afraid will happen to the d800 is that many wedding photographers won't need it as it is too slow and the files are too big, and many are already shooting Cannon, which has better lenses up it's line (don't argue). Fashion community might embrace it.
could not dissagree more.
The same could have been said of the 5DmkII. The D700 was faster and produced cleaner images and smaller files. did that stop the 5DII? How many weddings were shot with the SLOW 5DmkII? I'll tell you that more that I can count. It seems every wedding photog with a canon set had a 5DmkII and was ok with the speed. As you said, at 100% the 5DIII is clearly better and has ISO ranges that are not possible with the D800, althought the quality of these is questionable.
I suspect that downscaling a 36MP file to 22 will improve a the images about a stop or so just like scaling down the 5DmkII images to 12MP improves them as well. The argument was always made that the 5DmkII gave you the option to scale down when you needed it, and preserve high resolution when you didn't. The same argument now applies to the D800.
Ultimately, I think the biggest gains of the 5DIII are for sports and action photographers that need a lot of speed. Wedding and portrait photographers made livings with "slow" 5DmkIIs so why can't D800 photogs? With the cost per gigabyte always dropping down, 36MP files are not that much of an issue compared to 22MP files. It is just 1/3 more pixels.
So while I totally see that sports photographers will enjoy the new 5DIII over a D800, I don't think the new model has anything over the D800 and in fact, I think the lower MP for a market that is based on a lot of printing and cropping may actually make the D800 the better camera.