Upload & Sell: Off
I bought the sigma last week. I also own a canon 50 1.4, but I was never happy with the lens, because of focus issues on my 1Ds II (which doesn't have micro adjustment).
I put the sigma on my 5D III and found out my copy was front focussing on subjects nearby. On further distances focus was right. After micro adjustment of +20, sharpness was a bit better when focussing nearby, but not perfect yet. When focussing on distant subjects, it was now very soft. I didn't want to be changing MA in the menu while shooting a wedding, so I took it back to the store.
The other two copies they had in stock had the exact same problem and I asked fo a refund.
When I came back home, I took my canon 50 1.4 from my closet and tried it. After some MA (+10), the lens seemed to be much sharper than the sigma. I'm very happy that the 5D III has MA, because I can now use my old lens again.
This doesn't mean that the sigma is a bad lens, it just means that the store had 3 bad copies and I didn't get a good first impression unfortunately.