I think going for the inital 1-2 bullets hitting the head, and if they dont then follow through with the spray is one of the better ways to do it rather than just aiming for torso shots.
If you do get the headshot, you can save ammo and move on. If you don't hit it, you're already ready to spray control for the torso shots to kill. Either way, the person is going to die if you're aiming and given they don't kill you first.