Put in four.  After a few adjustments, you might be able to fit in five.  If you try to put in five new packings, there won't be any room left for the gland to register in the bore.  We use Lucas Red "N" Tacky; just put a smear across the surface of the packings that come in contact with the shaft before you put them in so that they have a little lube on first fire.  The packings are actually lubed by the water under normal running conditions.