EDIT: Link to my Flickr album of shots with this lens: https://www.flickr.com .../albums/72157667228291102
Sorry, no comparisons to my sigma - yet.
My focus missed a decent number of shots. I didn't count, but I would guess I missed about 60% - usually by approximately 0.5cm.
I'm not sure autofocus would have done better?
Focus ring is very pleasant with low tension, unlike the Sonnar 135 which I hate to focus with.
Edge sharpness is incredible: