Twins have lots of extra performance compared to quads, until one of the engines stops.
Hence at hot/high airports take off weight may have to be limited to leave sufficient performance on one engine.
Basically that means payload (and subload passengers) left behind, or less fuel carried and a tech stop (BKK) on the way home.
Jo's is 5500 feet above mean sea level, and with (southern hemisphere) summer temperatures it can become quite limiting for twin operations. From what I hear the 340-300 wasn't much better!