As I understand it, most pistol cartridges do not really benefit much from the longer carbine barrel compared to a full-size (5") pistol barrel. One of the exceptions to this rule is the .357 magnum; velocities are significantly higher from a carbine than from a revolver.
I owned a Marlin Camp 9 for a while. It was a nice little gun, but I decided that I'd rather just have a .22 for plinking/range use.
I watched one of those intelligence insulting specials on the history/military channel with Jeff Probst or whatever his name is, the former army ranger and air force para rescueman or some such.... and they mentioned the .45ACP got a fairly good sized boost out of the Thompson M1