If one ignores Avatar as it's run is just silly and ruins the fun for everybody the 2nd highest gross figures for movies from the 3rd W/E onwards are as follows:
3rd: Spider-Man Sony $45,036,912
4th:
Titanic Par. $28,716,310
5th:
Titanic Par. $30,011,034
6th:
Titanic Par. $25,238,720
7th:
Titanic Par. $25,907,172
8th:
Avatar Fox $22,850,881 3.0% 3,000 $7,617 $749,766,139 12/18/09
Okay seeing as Week 8 is when Titanic overtakes Avatar, it seems a good place to stop.
So when do people predict Avengers to drop out of the top two (essentially when will Titanic's Weekends overtake it (unless you believe its not making $45M this weekend).
For me, it is touch and go whether it stays ahead on Weekend 5, but weekend 6 it has no chance. (of course its still going to be over $200M behind TA's total at the same point so there's more fun to be had.)