There's been a lot of talk about how the 5D mkIII doesn't benefit landscape photographers. I searched for an appropriate thread to post this, but none of them seemed right. So here I am starting my first thread. (be gentle)
My reasoning is thus: I'm often shooting in the morning or evening (golden hour) in low light at an f-stop between f/8 and f/11 and quite often I'll be using various filters from polarizers to graduated ND filters. This means that in order to get decent shutter speed I generally have to crank the ISO up, but I want as clean an image as possible. So the 5D mkIII's improvement on the mkII's ISO will be a great help.
With the 7D I have no problem going to ISO 800 for a 24" print. I wouldn't make landscape prints that large from higher ISOs. But at most the 5D2 buys 1 more stop.
Will the 5D3 make an acceptable 24" landscape print at 3200? I'll wait to see the studio test samples from various test sites. But even if it can, this buys minutes under twilight conditions at best. After the sun sets shutter speeds rapidly drop with the light levels. ISO 800 or ISO 3200, your shutter times while stopped down with filters will still be in the motion blurring seconds range.
Perhaps the larger question is: will the 5D3 or the D800 make better large prints at 1600 and 3200? Everyone assumes pixel size drives noise yet that has not been the case for a decade. Technology plus total senor size drives total image noise. We have yet to see if the 5D3 has any real advantage over the D800 over their common ISO range. Even if it does at first glance, if your print size is, say, 24" from a 3200 file the D800 has pixels to spare in resizing and NR, so the end result would probably still be a wash.
Personally I would rather be able to reliably print larger without stitching. The D800 is starting to get into MFDB range. If Canon would just enlarge the 7D sensor to FF (45 MP) and stick it in a 5D body I would be thrilled.