Yup, that pretty well agrees with what I learned on this subject. The 400meter object is far from a planet killer, and the better prediction of impact area (if it does in fact hit) the better chances we have of avoiding a high death toll, as I mentioned in my #111 above.
This web site - http://www.space.com/scienceastronomy/astronomy/asteroid_paine_september.html
is easier for a non-scientist like me to understand compared with my earlier link. It gives the example of a 500 yard (bigger but in roughly the same ball park) asteroid producing a runup wave height of up to 120 feet at 1000 miles from impact. The actual wave height depends on the topography of the shore.