Thanks for the assistance, everyone.

Two additional questions: It's my understanding that if my upgrade clears <fingers crossed>, I should go through customs in T3 because the Flagship Lounge is outside of customs in T3, correct?

My outbound layover is about 4 hours, so I'm not too concerned about the time required for clearing customs vs. dealing with the bus & security. My return layover is only about 90 minutes, so it will be a much tighter connection. Does LHR have security lines reserved for elite members, or am I out of luck there?

Thanks!