The kill rate (as I understand it) is the last number in a unit weapon value.

ex.
stat_pri 3,0, arrow, 130, 30, missile, archery, piercing, none, 25, 0.45

Here I have it set to 0.45 (RTW's standard is 1). This controls the minimum delay between attacks (in 1/10th of a second) according to CA notes. Basically, a unit attacks slower. Most mods that I am aware of usually have a lower setting then RTW default. Someone else might elaboreate more...