Check out some of Philip Bloom's "People" videos. I think "Dublin's People", and "Sofia's People" were shot with that lens on 5DII's. Beautiful studies.
I don't usually post pictures, but when I do, they are of squirrels. Here's one solution to busy backgrounds: 500mm+1.4x. I think I went overboard with clarity on this one but it is what it is...
(Info: Cropped to 5x4 + rotated, 7D, f7.1, 1/160, ISO800, hand-held)