As predicted a few years back, the A350 will outperform the 777 because it is smaller, lighter, and more versatile. Furthermore, there will be more A350 performance surprises to come. For sure. Thx 777-X (an upgraded old aluminum plane ) won’t do much better than it already did. Although the 777x will do better than the A380 for certain, but it won’t go much farther. The 7771o is dead on arrival. Not many airlines will need those planes. Also remember, that many aircraft purchases are politically driven and the political climate and oil prices change.