This is more complicated than it seems. Not all mechanical heads are the same. You have to take into account cutting diamter/cutting surface, the bows KE, how the heads deploys and the type of game your after. At first glance with your set up as well as yourgirls is that you should pick a medium sized fixed blade head or one of the smaller faster opening mechanical heads. My website has some good info if you take the time to read through.
www.broadheadtests.com