There is a great article at Asprire Aviation about how the B777 could evolve. There is one part which could cause misunderstandings: the fuel burn comparison between the GE90-115B on the B777-330ER/777-200ER/B777F and the GEnx that is on the B787 (GEnx-1B) and the B748-8I/F (GEnx-2B).
Daniel Tsang suggests that the GE90-115B is more efficient than the GEnx and gives SFC numbers. Now, first of all, these numbers are for Seal Level Static (MN=0) Takoff. The relevant number for long-range