Thrust,
I can't say I'm familiar with the A340, but the B744 has a 5-minute limitation at take-off thrust. If we were to climb at Ref+10 and Accelerate at 3000' we would come very close to exceeding the time limit at climb thrust which is not set until flap 5 is selected (all engines). Ref+50 allows us to select flap 5 hence climb thrust. As this climb requirement is only for noise abatement, the radical climb profile is not necessary especially with stage 3 aircraft.