Take the velocity/energy list of the following:
.45 long colt, nominal bullet weight 250 grain 750/312
.45 A.C.P., nominal bullet weight, 230 grain = 835/365
.38 Special, nominal bullet weight, 158 grain. = 800/199
You will find that the velocity is pretty close for all three.
However, it is the energy that will increase. For the numbers above alone, a lot of folks love and live by the .45ACP. A lot of us, like me, like the .38, because of the package size, and carry ability.