that shot of the cowboy looks much like the stuff i've seen from the canon 50L. When the stars align just right, or wrong, things can look bad, but in my exp the sigma is just fine in the bokeh department. As i bet the 50L is also. actually, i'm not sure i've ever seen decent bokeh from any leica lens, but that's another topic.
my take on the canon 35mmL v2. it'll won't be released anytime soon, it'll cost somewhere north of 1800 US, it'll be just slightly better than the sigma and have weather sealing.
another thing is the build, the canon 35mm IS isn't really built any better than the old 35mm f2, and that wasn't very good. personally, i would have a hard time speeding that much money on it, esp with the great build on the sigma, but i stand by my first recommendation of choosing the lens based on your subject matter's movement, or lack there of.