Voyager Elite members (i.e Silver and up) have priority when allocating premium seats (upper deck on 744, exit rows, first few rows). In fact when you book on the Internet, only Voyager elite can select these seats.
How the fact that SAA is now *A affects this, I don't know. Best 'phone SAA and ask.
My own experience as elite Voyager has always been that I have been given the premium seats I requested.