I'm sure the actual gunsmiths will jump in here with better information, but I'll give it a shot while you wait for the experts.
In general an aftermarket match grade barrel for a 1911 will be oversized so that it must be fit to the slide. On a 1911, the sights are not attached to the barrel, so a tight fit between the barrel and the slide is important to make sure the barrel and the sights always line up the same way.
In addition, more care will have been taken to make sure the chamber is concentric with the bore, and that the muzzle is square to the bore. This is important to make sure the bullet both enters and leaves the barrel uniformly.
As far as Kimber advertising match grade barrels, and SA not advertising match grade barrels goes, I would take the advertising with a grain of salt. As far as I know, there is no actual standard for what a match grade barrel is.