Canon 5D Mark III Raw Image Quality
We used to convert raw files used for comparison crops with dcraw, an excellent freeware raw converter. Unfortunately, dcraw's author has not been providing timely updates lately, so we have switched to using Adobe Camera Raw with its noise reduction and sharpening sliders set to zero. We've found conversions made with ACR to be almost identical to dcraw, when dcraw's demosaicing option is set to match ACR's method.
Below are crops from Canon 5D Mark III raw files compared to raw files from other high-resolution full-frame SLRs:
Here, we can raw noise performance has been improved compared to the 5D Mark II, but not by as much as you'd think by just looking at in-camera JPEGs. The 5D Mark III's JPEG processing has improved as well. The Canon 5D Mark III appears to do well against the Nikon D800 at the pixel level, but keep in mind the D800's significantly higher resolution means that when printed at the same size, the D800 does better giving the Nikon the edge in high ISO performance. The Canon 5D Mark III performs better than the Sony A99, with the latter likely handicapped by its translucent mirror in the optical path.
Overall, an impressive performance from the Canon 5D Mark III. Noise is higher in very deep shadows, though, which is why dynamic range scores aren't as good as the Nikon or Sony's.