My argument for the heavier round comes from the LA shootout with the two perps wearing body armor and firing AKs. It only ended when one of them shot himself and the other had his legs shot out from under him. Even though the cops borrowed some AR-15s from a local gun store, leaving a couple of M1-As on the rack, they didn't seem to be able to penetrate the perps' body armor at the range they were shooting. An M1-A round (7.62x51mm) would have gone right through that armor and immediately stopped the subject.
A valid argument, when we're talking body armor.
Maybe we should offer a wide assortment of weapons for the trunk.
If that happens, I might be inclined to sign up!