For Emirates and other ME operators the high temperatures during the summer months have a very appreciable effect on payload that can be carried from around 1000 local time in the region. During these times the LR and ER twins are restricted in their payload due to engine failure on take off calcs whereas a 4 engine aeroplane is not.
I am aware of a scheduling department that refused to reschedule a 777 to an earlier STD on a non stop from UAE to YYZ and at STD the temp was so high the cargo had to be offloaded. By the time the cargo was offloaded and all baggage reloaded, around 15 minutes, baggage needed to be offloaded. Long story short it eventually left with nil bags and cargo.
For the rest of that summer the cargo payload was greatly reduced and the passenger load restricted as they couldn't move the STD forward without screwing up the connecting transfer traffic. The other solution was to schedule an A340-600 to the route and it could carry everything.