I'm not getting technical as I don't work like that when it comes to lenses. I simply shoot commercial applications and client work. I have owned the mk1 for ages and rented the mk2 during a desert fashion editorial to see how well it performed. My final assessment was simple...it's lighter and sharper however the jump in IQ wasn't significant enough for me to sell the mk1 and then pay on top for the mark2. I've never had a problem with sharpness and IQ from my mk1, always returned excellent images and with a little post Sharpening everything is on the money. Personally I preferred the extra weight and deeper sun hood. Mk2 is better but not significant enough for me. I found this the same for the 70-200 2.8L Mk2 also. My mk1 is tac sharp. Wouldn't sell either to upgrade, if it ain't broken don't fix it and if it does the job well then keep it.
