you should never run out of ammo if you have decent aim. and you are shooting one enemy in the head and then moving on. if you know you hit an enemy more than once, then melee them with a hit or two. yeah it can head shot multiple enemies but you can only grab one so what's the point? gun and headshot is the way to go. unless you're Jaki. even sherry's stun rod takes longer to kill enemies with than a handgun to face followed with a hit.
Knife headshot + melee is faster than aim+headshot+melee since with knife you only have to adjust one axis(aim up a little.) The extra range of the pistol is pretty meaningless when you are going to run up afterwards to melee them anyway. Using the pistol means you have to gather ammo as you go which eats up some extra time. Some of the pistols like Piers' or Stripper Cop's have some serious ammo issues because they don't reliably stun on headshot and quickshots take multiple bullets. Being able to stun two enemies at once makes it easier to not get hit in crowds while still getting headshot kills. Also predamamging other zombies means you get get 7 point coup-de-grace's on them. Bullet spam into somewhat distant zombies to save combos is also very ammo consuming but important for combing the stage to 150, especially if you are keeping the bosses alive till the end for the bonus.
