If you check out the Japanese grit comparison chart in the attachment within this archived post by smokintbird here it might be instructive. Helped me figure the shapton and naniwa stones out in terms of progression. They have a different system than the USA charts but use the same numbers. As grit goes up the differences increase to the extent that a 5k shapton pro or superstone is equivalent to an 8k norton. Make sure you open the attached grit comparison chart, not the post he links to in reference to something else. :)