According to my numbers,
The B747-200 first flew in 1970, has a range of 6900nm (with 366 pax).
The B747SP first flew in 1975, has a range of 6650nm (with 276 pax).
These numbers make me ask why the 747SP was built at all. There was an aircraft that had already been flying for 5 years that had slightly more range and greater capacity. These numbers seem to rule out the justification of the -SP for long range flights, as the -200 could fly farther. Maybe it was more for lower capacity then range?