Here is a nice site from Asus, for the Asus z87 Motherboards (mainly the ROG but will apply to others) and how to overclock both the CPU and DRAM/Timings and what all the options mean, stand for and how and what limits to adjust in.
http://rog.asus.com/242142013/maximus-vi/maximus-vi-series-uefi-guide-for-overclocking/
http://rog.asus.com/242142013/maximus-vi/maximus-vi-series-uefi-guide-for-overclocking/