DDR2 533 1 GB or CORSAIR DDR2 667 2 GB?

The motherboard I am using indicates that a DDR2 667 memory may be used with it. Does that mean it is the maximum memory for that motherboard? Furthermore I am currently using a DDR2 533 1 GB. Can you tell me if performance would be better if I replace the DDR2 533 1 GB with a CORSAIR DDR2 667 2 GB?
