To attempt a response to Tommyinwork: Airbus's equivalent to the B757-300 in terms of capacity is the A310 which is still, nominally, in production but is non fly-by-wire and CCQ. They have talked for years about "shrinking" the A330 to fill this gap but it would be quite a heavy, uneconomic aircraft. I don't know if the A321 has any further stretch left in it - others may know. Boeing's equivalent to the A340-600 is the B777-300ER which has about 30 less pax but flies about 300nm - further burning a lot less fuel in the process.