been asking myself which is better in color rendering.... this beast or the 70-200 f2.8 IS II? i think this image answers my question.
At 135mm the 135L stomps on the 70-200, it's sharper, has faster and more accurate focus, renders better detail, renders more contrast, and renders more colour. It's also lighter and takes up less room in your bag.
At all other focal lengths the 135L is total crap and the 70-200 wins.