I do expect Spidey 3 to fall. There is no way around it. Within mere weeks Shrek 3 and Pirates 3 will be out. It won't have the legs to survive. But it will still do 300 million(at the low end however) + something F4 2 CANT do. F4 2 at most will hit 200 million and even that is pushing it. People wont be ready for another marvel film a month after Spidey 3 and F4 1 was not well liked.
Shrek, Pirates, and Spidey will all do somewhat less than their part 3's purely due to them all hitting at the same time. The studio's are fools for doing this. It is boxoffice suicide.
The days of summer long boxoffice legs are far dead. The window is 4-6 weeks at most now to make money. Pirates 2 proves you don't have to be out at the start of summer to do well. Really stupid move pilling everything into may. Either dreamworks should push Shrek into late July or Disney should push Pirates into late July.