Just got myself a Canon 50mm f1.4 to replace my rather lacking Sigma 50mm. The difference is pretty damn huge. This lens completely triumphs the Sigma, it can properly do 1.4! Although you do need to watch out for fringing and CA at this aperture!
Also tried the f1.2 while I was testing the f1.4. These two lenses are seriously similar at f1.4 and out.
Braking the rules a bit by posting three pictures.

(Unedited - Except for white balance)


f2.0
1/1000
ISO-200


f1.8
1/5000
ISO-100


f2.0
1/8000
ISO-100