Pro’s Twins
We run twice daily flights from Asia to SFO. One is with a B777-300ER the other with a B747-400. Over a four day period the B777-300ER burnt 26.7% less fuel than the B747-400 for almost the same payload. Add in the significantly lower maintenance costs of the Tripler the 74 isn’t even in the race.
Con’s Twins
We operate a daily flight from Asia to JNB which has an elevation of about 5500ft. While the B777-300ER isn’t currently being used on this sector, when it is, it’s generally only used during the southern hemisphere winter as the OEI second segment is too restrictive to make it consistently viable without a tech stop in say BKK. As an example, on a 30°C day there is about a 50 Tonne payload restriction without a tech stop.