I'm surprised Bryan had such difficulties with obtaining a good copy of this lens, especially since Roger at LensRentals.com seemed to get a whole stack of great copies. Maybe the UPS man decided to drop the packages with the first two copies he received (I had to have a talk with my UPS man... it is not acceptable to throw packages at my front door from 5+ feet away).
The copy I received seems almost as sharp as my 70-200mm IS II at 70mm and also seems just as sharp across the rest of the focal range. It's vastly superior to the mark I lens I had in sharpness and autofocus, so I'm a satisfied customer.
Not quite sure why you'd want to replace the 16-35mm II with this lens... these two lenses seem to compliment each other more than compete. I know I'd really miss the wide end of the 16-35mm, but I suppose your focal length needs might be very different from mine.