Ford Airlane, use of full reverse thrust will not reduce your landing distance if autobraking is used - and I'm sure that most pilots will use autobraking as per their company SOPs as opposed to manual braking, esp at a hot/high place like Jo'berg. This is beacause autobrakes set a measured decceleration rate as sensed by the IRSs. Application of reverse thrust above idle will result in the IRSs releasing the brakes a bit to maintain the set rate. You will only decrease the landing roll if you manually brake, and this will probably result in increased brake wear on carbon brakes for the reasons stated previously in this thread.
For those who are interested by the boring details, these rates are 2 feet per second/per second for autobrake 1, 3 fps/s for autobrake 2, 4 fps/s for 3 et seq.