To follow up what I'm saying. The following are similar (loosely) films, with their corresponding, adjusted opening, on a per theater basis.
Spiderman: 31,768
X2: 22,871
Batman forever: 24,757
Batman returns: 25,231
Batman and Robin: 18,470
Batman: 28,304
I would say that 23,500 is pretty safe, and, considering the way the box office is going this year, I would even venture out to guess 25,000 per theater. If I had to make a prediction right now, I would say around $85mil on it's opening weekend.
JP