I'm interested in this lens for use on a 1D Mark IV and a 7D. I work mostly in the super telephoto range, but it'd be nice to have these focal lengths covered too. I will say that I already own the 17-40 f/4 and the 70-200 f/4. But I like the idea of IS, which the 17-40 doesn't have. Any reviews from BPN members would be greatly appreciated.

