We need to wait for next year, but now my thoughts are so. I can change my mind, but not now.
Lets imagine one situation with Spidey 3 making $60m opening day and $140m opening weekend. Whats then? How much will it make? Will Shrek 3 or Pirates hurt it?
I'd answer no, but if it really makes $140m opening, it can get to $420m in total.
So it means that it will hurt Shrek 3 and POTC3. But also it means that POTC3 won't make more than $330m, because most people will go to see Spidey 3.
And again, POTC3 has Memorial Day, so I doubt there can be 2 movies in one month, which will both make more than $115m.