Since some have found my original files useful, I was shooting some for my own comparison (this time paying more attention to focus accuracy) and thought I would share.
As with before, these are just random "walking around snaps" - not meant to be artful photos, but to compare these lenses against one another in different scenarios.
I paid more attention to focus this time, and found that there are instances in which both lenses "miss". I used center (1 PT AF) in all instances, and generally framed my shots so that the focus point was pretty much dead center. I just took one to two shots of each subject/scene each time, so it wasn't a matter of picking "the best", but just making sure focus was complete (red flash box) and shot.
All shots were at f/1.4 except for a couple of the exterior shots (landscape) - see EXIF for those.
A few were shot in a very dark utility room (the water timer and hanging keys) and some in medium light.
This time I shot in RAW, and I will put all of the original, OOC RAW files on DropBox shortly.
Again, I had the Canon 50mm f/1.2L on one Canon 5D Mark III and the Sigma 50mm f/1.4 ART on another Canon 5D Mark III. And again, I manually adjusted shutterspeed but had both set on Auto ISO.
I have not adjusted/micro adjusted either lens to any of my bodies - just at default settings.
These are the versions saved down to 1024 wide in Lightroom (otherwise as shot OOC)...
One observation... when I shot in camera as JPEGs, the Sigma was much more vibrant. This is true as RAWs too, but... looking at the images saved as JPEGS, looking at the second set below (the bowl of blood oranges), the Canon looks much more vibrant than the Sigma, so they don't translate into JPEG (via Lightroom) in the same way they do when shot in camera, if that makes any sense. As I scrolled my preview for this post, I thought maybe I had misordered them, but it is Canon on top and Sigma below... If you pull my RAW originals off Dropbox (link soon), you'll see what I'm talking about.
In each case, CANON is the top image and SIGMA is the lower image in each set: