What are the "high performance characteristics" of a Boeing 777? News of the potential further stretch of the A350-1000 have seen pretty much all journalists discuss the "high performance characteristics" of the competing Boeing 777-9 with Middle Eastern airlines. For example:


  [...] the new Airbus jet would target airlines that need high-capacity, long-range aircraft but not necessarily require the same high-performance characteristics that have made the 777-9 so popular with Middle Eastern airlines. (The Gulf region can be hard on an airliner.)


What exactly are these? Why is the 777-9 suited to them and the A350 not?
The gulf region is very hot, something that can reduce aircraft performance. The 777-9 is better able to cope with that (due to the higher thrust from the engines and larger wing area).