OC is overclocking; running components faster than they are meant to. Read before doing.
SLI/CF are nVidia and AMD's ways of running two or more GPUs in parallel to render faster. With your budget it would be future proofing to let you add a second GPU later.
Thankzz for this (i should have made my question clearer need some help on what i should get) any recommendations on what i should get
HDD ... and stuff