IMO it's a situation very similar to the "Narnia vs HarryPotter4" box office derby.
Actually Superman is Narnia and POTC2 is Harry Potter.
Harry Potter4 was the sequel of a recognizable franchise with millions of fans.
Narnia was relatively "new".
HP4 had a great impact at the B.O durinh the first week-end. : $102,685,961
Narnia had an average impact: $65,556,312
But in the total gross, Narnia did $291,710,957m and HP4 $290,013,036.
WW won HP4 with $892,213,036m against the $743,710,957m of Narnia.
Great results for the first Narnia movie

Was it because of the fantastic Disney's marketing?
I don't know, probably only because kids liked Narnia (and I don't understand why

).
So, IMO, if the marketing is going to be really good, I can see SR to have in USA numbers very close to POTC2.
WorldWide the battle is impossible

Sequels with beloved actors always win.