.30 Carbine is much faster and flatter shooting out of a rifle than a .45 ACP carbine. So, even if due to hypothetical bullet designs, stopping power for the two rounds was equivalent, the .30 Carbine is going to have the advantage of making hits at longer ranger than .45 ACP.
For example, I have a Marlin Camp 45 and an Underwood M-1. When shooting the Marlin at 50 yards there is a perceptable lag between the time I pull the trigger and the sound of the bullet hitting the berm. There is no such lag with the .30 Carbine because the velocity of the .30 Carbine round is roughly twice that of the .45 ACP even when the latter is fired from a rifle.
As a civilian rather than a GI, I have the option of using expanding bullets in my defensive arms. In this case the .30 Carbine still retains an advantage IMO, because a 110 grain JSP at about 1900 FPS MV is going to do more damage than a .45 JHP at about 950 FPS MV, especially if the range gets stretched beyond 25 yards. But even with Ball, I'd take one of my M-1 Carbines over my Marlin, an M-3 or a Thompson if TSHTF. I feel more confident in hitting my target with a Carbine if the range gets past 50 - 75 yards.