Recent motherboards seem to run faster RAM at DDR3-1333 (PC3 10600) by default. You'd have to set your BIOS settings to use the XMP profile, or manually set the RAM frequency and timings.
You may wish to read this:
AnandTech - Sandy Bridge Memory Scaling: Choosing the Best DDR3
The short version is that there's little to gain above DDR3-1333, outside of synthetic benchmarks.