I seriously doubt that your BIOS allows you to modify the 'DRAM Frequency', and if it did look at the 'SPD' tab, more than likely DDR3-1333 (667MHz) is at CAS 9. The 'real' performance difference running DDR3-1333 CAS 9 (slower) vs DDR3-1066 CAS 7 (faster) is fractional. You'd gain in the real world nothing; i.e. leave it alone.
There's a difference between different RAM frequencies being 'specified' as compatible vs 'running' and working at the higher frequencies. RAM's speed as shown below is BOTH a function of Frequency (higher=faster) and the CAS aka pauses (lower=faster).