The following figures from the performance manual:
A/C model A340-313
Manufacturer's Serial Number 0194
Engines C4's
MTOW (Structural) 271 000 kgs
Takeoff conditions:
Runway 03L full length Johannesburg International
Config 2
Packs off
Anti ice off
No wind
Dry runway
At 20 degrees C:
Max takeoff weight 262 400 kgs
Limited by obstacles and brake energy
V1=136
Vr=158
V2=165
At 30 degrees C:
Max takeoff weight 244 200 kgs
Limited by runway length and brake energy
V1=140
Vr=157
V2-163
As can be seen from Cpt Underpants' posting, their A340-300's in CX have differences in the structural limits. We also have some with a Max structural take off weight of 257 000 kgs and with C3 engines (less thrust).
With this in mind one would have to know the exact details of the SAA aircraft to see what their limitations will be, and more importantly what their effective payload would be on the various sectors.