By default X58 and i7 920 run memory at 1066mhz. You'll need to go into the BIOS and change the default memory multiplier from 2:8 to 2:10, that should equal to 133mhz x 10 = 1333mhz RAM.
As for the rated speed: The SPD chip on your RAM provides a number of potential settings, and your computer's Bios has chosen the default. If you don't like that it's showing a different number, then set your memory divider appropriately. 2:10, as Flyin indicates.
As for any difference in speed... You may not want to bother, since there is little/no performance gain associated by running higher clocks: