bukjuice, if you know how fast your wife's bow is there's a simple calculation to determine K.E. the wt. of the arrow times the velocity times velocity divided by 450240. that will give you the foot lbs of K.E. the arrow has leaving the bow. I want to say stay above 26ft lbs of K.E. It also depends on the type of broadhead she's using a cut on contact like the magnus stinger will be heads above mechanicals in which you would need closer to 40 ft lbs of K.E. my friends boy shoots a micro midas set at 40 lbs and about 310 gr. arrows which works out to be 26.18 ft lbs of K.E. and he had a complete passthru on a decent sized iowa buck. hope that helps