Very well, I'll add that. However, a better bonus supercedes an old one. Therefore, if you have 6 kills, so +6 bonus, but then you do-in a group of 5 undead, you're at +11, since the undead bonus supercedes the normal one, even though its maxed.
^This path also works for pallies, btw, although it probably works better on a cleric (with the whole "healing" and "undead smiting" theme...)