There are no "Extremist Salafis" in actuality. A Salafi is one who is upon the Path of the Prophet,his companions and the pious predecessors. Hence a person is either a "Salafi" or an "extremist" I believe the word you are looking for is "Salafist" this is a term used to describe an extremist who wrongly believes his beliefs and methods are in accordance to the Quran and Sunnah.