In addition to what o1die stated, unless you buy a matched, tested RAM Kit, there is no guarantee that several of the same DIMMs will function without issue or that they will run at the advertised frequency for one or a pair of DIMMs. DDR3 in particular can be quite fussy as the frequencies continue to increase. That is why it's best to buy a matched RAM kit.
My testing shows less than 1% diff in system performance between 1333 Mhz. and 1600 Mhz. RAM frequency.
If you want to try CPU OC'ing the tutorial at the link below should help.http://www.overclockers.com/forums/showthread.php?t=596023