Got together with a friend of mine this weekend for a sunrise shoot. He's got the 50L and knew I'd just picked up a sigma, so we decided to do a quick comparison... We were both curious to see how the sigmalux looked -vs- the 50L. These were very quick tests done on my body as I have a tripod and bracket. I AFed on the EOS/5D logos on the side of the body and then fired off then entire sequence (so only AFed once). Matt's 50L backfocuses (something we only realized once I got home with the images) on my body so watch the pentax in the background for the sharpness on the L and the bag in front of the logos for the sigmalux. Also notice the wider feild of view with the siggy? Otherwise they're pretty similar IMHO...
These were run through my basic LR export action, so they have some slight adjustments... But I do have FULL RES versions available (they were also shot as JPEGs). Read the note at the very end for instructions on how to view the full res images.
50L @ 1.2