As Dr Ashby's broadhead penetration tests on African game showed, neither KE nor momentum can be used directly to predict penetration by a given arrow, it is only a magnitude indicator of POTENTIAL penetration capability(i.e. all else being equal, the more you have of either the more penetration you can generally expect).

Even in game Ashby showed there was a signifcant relation between the size of the broadhead ferrule and the arrow shaft(larger ferrule then shaft size increased) and the broadhead type(cut on impact etc).

Shot selection, stability of the arrow on impact(tune), broadhead failure etc all play important parts in penetration.