The overload issue should be easy to settle by a QAR/DFDR download. The Airbus' three flight control computers weigh the aircraft after liftoff -- too bad that can't be done while taxiing -- and these values can be displayed on the MCDU. Usually the variance between the three are only a few hundred kgs, which on a +300 ton aicraft speaks to their accuracy.
Let's just hope that the cause of this incident was not flap mis-selection, i.e. 2 instead of 3.