RAM overclocking is quite complex, and doesn't have as much a reward as CPU or GPU overclocking. Most people typically don't bother as its not worth the time to figure it out.
Typically a faster frequency has a greater effect than lower timings.
Also if your using an Intel chip, be aware that there is a 1.55v cap on memory voltage. Go over that number, your placing excessive strain on the CPU memory controller which could damage it over time, as well as voiding the chips warranty.