If you have ever asked for advice on what type of RAM to purchase, you were probably given a response that goes something as follows. The higher the supported bandwidth of the RAM, the better, but having lower timings is also important. Both options of course bring along price increases, and buying cheaper "generic" RAM is seldom recommended. The old adage of "you get what you pay for" is often used.
Anandtech has put up a detailed technology overview about RAM
(Random Access Memory) which should give you a pretty good idea about the inner workings and explain in current terms why certain memory is effectively faster than other.