Variety has a discussion of how high it might go. The takeaway: They think the #2 spot and maybe even a $500M domestic cume are in reach.
One small quibble: The article seems to suggest that you can't compare Dark Knight to Titanic because it was a different economic era and no one could do that again and blah, blah, blah. Don't believe it. Titanic's success was firmly grounded in the same economic realities of today, where movies had to open or perish. The opening weekends of the time weren't as big, because of inflation and smaller screen counts, but it's a difference of scale, not of kind. What happened with Titanic was totally unexpected and totally unpredictable. It was the type of singularity that only happens once or twice in a generation, when a movie becomes part of the culture. The fact that Dark Knight won't do that kind of business has nothing to do with changes in the marketplace and everything to do with audience reaction to the films.
Just for fun, take a look at this chart of Titanic's weekend grosses. It was in release for 19 weeks before it experienced a decline of more than 26 percent. Heck, during that period, 4 of its declines were in the single-digit percentages. And on six separate weekends, its box office take actually increased.
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