The other side, mentioned above, is that your processor may be incapable of running the ram at spec. The ram can do what it's rated to, the processor is rated to 1333mhz so anything over that is lucky (i.e. overclocking) according to intel.
You're going to have to play with the bios to get more out of your system. If you're not overclocking the cpu, leave the ram at whatever speed it's running at now and put the money wasted down to experience. More ram frequency is going to do nothing measurable for performance at any point, worrying over it when the processor is running far under its potential makes little sense.
Or, better, clock the cpu as well as getting the most out of the memory.