Also, when overclocking to reach the level of stated overclocked memory speed ability. You may find as I have, even if the motherboard supports the overclocked memory you may find a problem with stability when trying to reach those speeds. Depending on your memory, motherboard, timings, voltage , VTT on the CPU, may different factors come into play when overclocking memory. My personal experience has shown me with my current system that using XMS3 Corsair memory has come to be a problem.
Although I am able to reach overclock speeds of 3710 Mhz on my I5 750, The highest overclock on my Corsair 1600mhz stable is 1484 Mhz. Also, I am unsure and still researching that the issue may lie with my CPU being able to handle that high an overclock even when adjusting VTT.
Overclocking can produce some frustrating results, but it can produce some exciting results.
Be sure your processor is rated above 1336 Mhz FSB or QPI. Be sure when adjusting VTT, Vcore as well as memory volts to stay within the manufactures specs and watch your temps.
Just as stated above Ratio and multipliers have much to do with stable overclocks.
Research you system capabilities and be sure you know the limits of your system before you start to overclock. That way you will have a good idea of the max able specs you can overclock.