Confused about the comment above - I understood the SP was developed for extra-long-range flights, and SAA was one of the airlines most keen for it BECAUSE they could get round the bulge.
-- Mike
You are correct. Pan Am was the launch carrier and the SP was developed to serve thin routes. 'SP' literally means "Special Performance". It also had a higher cruising speed. Same cockpit meant that pilots could swap with any other 747 currently in use at the time of development.