There is really no such thing as a "one shot stop" for a combat pistol round.
Each caliber has it's advantages and disadvantages, as has been discussed in depth on this thread.
But to expect consistent and instantaneous stoppages from a pistol round is absurd, as there is no combat pistol cartridge that will do that.
Is a single FMJ round from a .45 better than a 9mm? Of course.
Are two rounds from a 9mm better than a single round from a .45? Perhaps.... depending on shot placement.
And so on....
But personally, I'd lean towards them going with .40 S&W. That cartridge gives you a lot of latitute in bullet weights, and 50% more rounds than the .45 ACP pistols.