I flew B747 100, 200 and 400, for 18 years copilot and captain. If the 3 engine stabilised cruise before crossing was FL340, it doesn't sound as if the aircraft was that heavy. We lost an engine over the Labrador coast in a -200 and continued to Chicago at FL250, climbing up to FL290 before descent. We calculated we had just enough fuel to make it at that level. In this case, a perfectly acceptable decision (in a 747) as long as the fault is known and confined. As stated, the only reason for the emergency call was having to make an involuntary descent. Maybe only those who have flown the 747 understand what a small issue it is? Back in the 70s, we got used to losing an engine up to twice a year. Flying the -400 up to 6 years ago, the RB211s were performing superbly. That would have been a factor in continuing the LAX-LHR flight from a failure in the climb, a decision any of us would have happily taken. Incidently, the severe FAA reaction was withdrawn as they were not justified in their comments, and the crew was strongly supported by the airline.