Try this:
http://www.ballisticsbytheinch.com/45auto.html
Note that the maximum velocity for each different cartridge is not always achieved with the same barrel length. For example, the first one listed (Cor-Bon 165-gr +P) keeps increasing right up to the 18" end of test. However, skip over to the next-to-last entry (Federal 230-gr Hydra-Shok) and it gets maximum velocity out of the 11" barrel, and from there the velocity decreases as barrel length increases. But this experiment used all premium self-defense rounds. I suspect that a standard 230-gr FMJ loaded more or less to military specs (approximately 830 fps out of a 5" barrel) would also peak at less than a 12" barrel, and would see velocity fall off considerably thereafter.