I love analyzing the box office, so this question is rather interesting.
In my opinion, Iron Man doesn't stand a chance. I wholly expect TDK to tally $120+ million on its opening weekend at minimum, and I also expect that it will become one of the highest grossing films of all time domestically, i.e: in between Spider-Man and Dead Man's Chest, although it could fall a bit short of $400 million depending on certain factors.
Of course, these numbers of mine are only really a result of everybody saying the film "lives up to the hype and then some". At the end of the day, you need a truly great film to live up to the hype of its opening weekend. Spider-Man 3 wasn't able to to do that, because in terms of legs in correlation with its opening weekend of $151 million, it should have crossed $400 million without breaking a sweat, but the film wasn't deemed that good so it fell considerably short.
I'm not sure about the international market for TDK at this moment. I don't see why it couldn't make $350 million or so overseas.