I think with the long colt you would maybe find a gain of 200 ft per second. I have a Marlin Camp carbine in 45 ACP,when we compared chronographed pistol loads to the carbine's readings the average velocity increased by 160ft per second.
These lower powered pistol cartridges do not need the full barrel length of the carbine to achieve maximum velocity and at some point the bullet will actually start to slow down through friction.
With the 357 and 44 magnum calibers you have such an increase in powder capacity that they can take advantage of the increased barrel length and velocity increases of up to 500 ft per second with some bullets could easily be obtained.
Murray