I don't 'shred' , - more a daily quest to improve general dexterity, but it's four fingers every time for me.
I picked it up off of the 'one fret per finger rule ' guys like B.B.King, Larry Carlton - and other jazz infuenced precise players. I find the discipline of that ( and trying to keep the thumb in line with the back of the neck / not letting the edge of the little finger touch the edge of the fretboard e.t.c.) keeps me mentally focused - and my movements economic. :)