From what I understand of the mechanics of the inertia system, the M2 will fire better the more give the stock has i.e. the more movement occurring in the gun, the better. That being said, it seems that if you pad the stock enough, the recoil between the two guns shouldn't be a big difference? This is all theory of course as I'm trying to understand it better myself.
Also, make sure the gun fits your wife. I'm considering between the two and the versamax doesn't fit me right.