What I would give to have the 5D mark III as my workhorse camera and the Nikon D800 as my dynamic photo shooter. I shoot weddings and the mark III is the jack of all trades with great low light, fast shooting, awesome video, more convenient file sizes with more than enough resolution, great screen, 3 custom modes, and just overall awesome pictures. However, there is no denying that in scenes that have great lighting with plenty of DR, with a style that looks good super sharp, paired with a great lens, and shooting at lower ISO speeds, the D800 will yield a noticeably better photo when placed side by side. During portrait sessions, I do shoot some photos under those conditions that would make for some really stunning pictures using the D800. However, all of that comes with many weaknesses such as huge file sizes, not quite as wonderful (but still good) low light results, and slow speeds that keep me from wanting it as my primary shooter.