Jim C - it's a complicated world! I don't think we ever plan for that 'double emergency' you quote. In addition, it is often the case (depending on engine design) that the higher RPM with a single engine may produce a more efficient engine than 2 running at cruise RPM.
It is worth everyone remembering that the whole ETOPS planning thing is just that - a 'thing' used to generate circles on a map you stay inside. What you do when 'it' happens is, as we are all saying, down to that well-worn 'airmanship' thing.
If bucker's regulatory authority have approved Mmo so be it - look on the bright side - at least bucker will be 'up' on fuel if he/she flies at more normal speeds on the divert
