I agree with the angryblackman and everyone else for that matter.
Stay at BA! I have a very good friend who is at BA and he is an American
who as a new hire started in the 777. That would never happen at a U.S. carrier. He is also quite a bit older than you are and will probably never see the left seat at BA and he couldn't care less. It is better at BA as a f/o than at many (not all mind you) US carriers as a Captain.
Now if you can figure out a way to get us American's over there at BA
(without marrying a Brit that is).
RDG