Latency is the time delay and also called as PING . It is mostly measured in ms. Typically,For gaming Pings from 20-300 are considered as playable.
Overclocking means that you are increasing the stock clock speeds with whatever you want.This can mean a added boost to your processing/GPU card's Power but keep in mind that you need to cool your product and it voids the warranty.
More information on these topics :
http://en.wikipedia.org/wiki/Latency
http://en.wikipedia.org/wiki/Overclocking
Yes you can overclock your graphics card using a software such as ummm Riva Tuner.Google for more options.
I think it would be a little bit Risky to overclock your RAM, also in computing terms, you should never Write RAM as Ram .
over clocking/Latency
Linear Mode
