G Y S
I'll stick my neck out....I can't speak for the Roller -300 or Emirates ops/procedures but by way of illustration for the GE -300 at 50 celsius, sea level airfield, the landing climb limit weight ( for a flap 25 or 30 ldg) is just under 300 tonnes, that's vs. a normal max landing weight (for us) of around 250 'ish tonnes....
In other words as you say with all running normally, at the end of a normal sector, at normal landing weights the performance manual would have you believe the -300 GE at least would have had plenty of power available to cope with most things that could be thrown at it....
At the risk of verging into speculation I wouldn't expect the Trent engined version to be grossly different, the 300's don't have a reputation for being under powered......