Do they travel faster and shoot flatter, well not really. It all depends on the load you pick. Some 2 3/4 inch loads are as fast or faster than some 3 inch loads. You have to look around and make sure what you are buying.

It really depends on what your gun likes. If you take the same load, but one in 2 3/4 and another in 3 inch your gun may prefere one over the other. The only way to know is to try them.

What kind of barrel are we talking about, smoothbore with an IC choke, or a fully rifled barrel shooting saboted slugs? The newer saboted slugs that use the pistol or muzzle loader bullets normally have better trajectories and performance on game regardless of the shell length. Some of the 2 3/4 inch shells are around 1900 fps.

I honestly don't see a need in using 3 inch shells unless your gun shoots better with them. You sort of have to experiment.

Paul