The images are really what you'd buy the Canon 6D for. Long story short: They're outstanding. For anyone who's only shot previously with smaller sensors, full-frame images will be a revelation. Photographs are richer, with more detail, color and depth of field.
The Canon 6D captures a very high 2600 x 2400 LPH (vertical and horizontal) amount of detail on our resolution chart. In general, images are very clean and stay that way into the high ISO ranges. The first sign that noise starts to smudge details start from ISO 1600, and we'd say that images remain usable up to ISO 25,600 (the native limit) if you're willing to clean up or endure some noise (or are showing images online).
At ISO 51,200 there's too much visible noise, but the 6D handles image noise admirably - it's kept to a minimum and most of what appears is luminance noise, with little to no color noise. Except for the fact that the 6D produces a slightly smaller image at 20.2MP, noise performance looks virtually identical to the 5D Mark III's 22.3MP images.
Of course, with the 5D Mark III, you're paying for more than just ISO performance. While the 5D Mark III can capture up to 6 frames per second, the 6D does a slower 4.5 fps. Respectable? Yes. Slower than the Nikon D600's 5.5 fps? Also yes. We've already covered AF performance in the previous section, but it's worth repeating again that the AF speed and accuracy is very good, even in low-light. However, you will be hindered by the small number of 11 AF points and the limited coverage available.
One minus point that might dint perfectionists is that the viewfinder only offers 97% coverage. What this means is that the viewfinder can only show you 97% of what will end up being your final photograph, so you might see unexpected elements show up in the 3% you couldn't see in the frame. Some might not miss it, but part of the appeal of full-frame cameras have been their large, luxurious viewfinders with 100% coverage, so it's nit-picking but still disappointing.