I shoot with both a 7D and a 5DMkiii. I currently have a 70-300mm f4.5 - 5.6 DO IS USM, and am wondering if I should upgrade it to a 70-300mm f4.0 - 5.6 L IS USM or the 100 - 400mm. I have found the current lens a little soft on both bodies, certainly when compared to my 24-105L and even my 15-85 EFS.
The 100-400 has the attraction of an extra 100mm, but then it is a much older lens. My main use for this historically has been bird photography, and therefore it is better on the 7D. Can anyone comment?