I've read that some use non file fit rings that are .005 larger than your bore size. If they give you the gap you want, then the rings will give you a better seal than rings that have been filed a lot. The article also said that different brands of rings may vary slightly, which will affect end gap.
Even if they are just a tad too big, they may only need grinding a very small amount. What the guy was saying is that the less you cut off the ring the more of a perfect circle it will make, which will provide a better seal than a ring that has had a lot taken off of it. Makes sense to me.
