Granite surface plates are found in machine shop tool rooms. They are usually flat to at least .0005 inch, and can be much more. The easiest way to compare abrasives is to compare the particle size in microns. The x-fine DMT is 9 microns, as is the 2000 Japanese, and 4/0 emery cloth. The japanese stones have the finest grain structure that I am aware of, a 10,000 Japanese stone is .3 microns. Do you know which system your papers are rated in? I like the idea of having inexpensive paper that I can just toss when it's used up.

Dave