Quite a long time since I went back-n-forth over the N Atlantic in 757's & maybe the law has changed; but, loss of an engine on a twin engine aeroplane is defined as a 50% power loss and, therefore, a Mayday situation. Next, probability is that the aircraft cannot maintain height and must descend whereafter the single engine is operated at MCT. Now, lower level, MCT and a Mayday...........for 5 1/2 hours......., really ? I mean, honestly ? GOSH !