They should all put exactly the same sized holes in a car body, wouldn't you think?
To WebleyMkV, while what you say is correct in that a faster burning powder is more efficient in a shorter barrel, because it's more likely to all be burned within the barrel, I don't think that's necessarily the way to measure efficiency. It may or may not be true that the faster burning powder will produce a higher velocity, though it will probably produce less muzzle flash or blast. I would be more likely to believe that a heavier charge of slower burning powder may in fact produce a higher velocity even at the cost of less efficiency as far as burning powder is concerned. Even so, there's more to it than that.
If you have a variety of handguns, particularly of the same caliber, you may not want to customize the loads that much. In other words, there's no point in having the same caliber if you use different loads in different guns, though I still understand the object. One might want to use different loads even though you only had one gun. In addition to having a load suitable for shooting 1957 Chevrolets, which would be detestible, you might still have use for wadcutters in your pet .357 revolver.
Ultimately, you can only measure the efficiency of the load by measuring the velocity of the load--in your own gun. That's true for factory ammo, too, about which you may not know anything about the powder. Of course, muzzle flash and blast can still be a concern that you will still want to take into account no matter what the velocity comes out to be.
Shoot low, sheriff. They're riding Shetlands!
Underneath the starry flag, civilize 'em with a Krag,
and return us to our own beloved homes!
Buy War Bonds.