I recently heard a new idea when it comes to the 9mm vs the 45 acp. There was always the fast vs slow..heavy vs light...high cap vs lower cap arguments. The new argument is "energy levels."
According to an article in the 2008 Gun Tests Buyers Guide, Bill Davison states, "...The whole gun is in the fight, not just one round, so when we are looking at energy levels, we should look at how much energy is in each pistol." So. if you have a standard 1911 with 7 rounds, the pistols has 7 times the energy of a single bullet, one energy level per bullet. A CZ 75 in 9 mm holds 16 rounds and therefore has 16 energy levels and 9 more then the 1911 and is able to stay in a gunfight longer.
Interesting idea...