The SOs on the 777 will fly all variants of it, but there is only one non-ER trip that uses SOs: Bahrain. Since there are so many 777 SOs now, expect to fly zero to one BAH trip a month.
Compare that to the three 777 SOs who started 2 years ago who flew Bahrain exclusively... what a life, eh?
I think another pro for the 777 fleet is that you have younger captains and apparently none of the long-sleeve brigade.
SW