From what I have read, Chasseur d'Image "gave five stars all around to the Konica 28/2.8 and only 4 stars to the new Emarit 28/2.8 though the latter is a far better lens optically and functionally."
Same question posted here: http://photo.net/bboard/q-and-a-fetch-msg?msg_id=003tSQ
I own both the 28 Cron ASPH and the 28 Elmarit ASPH, and would love to own the M-Hexanon 28mm. Only problem for me was the inability to code permanently, otherwise, the Hexanon lens, when I was trying to decide, is pretty good. Distortion is more than the Elmarit and Biogon but this is relative to each other. Build, flare resistance, sharpness, etc are all there.