A quote from another post of mine...
The fist number in your RAM timing is your CAS Latency, or CL. It is the one that determines the speed that information can be retrieved from the RAM in clock cycles - of course, if you double your speed (800MHz to 1600MHz) but half your CL (CL 6 to CL 12 [half speed is a number twice as big]) your RAM is going to retrieve information just as fast. The only benefit is that as your MHz goes up, you get more bandwidth.
Hope this helps.