I use planes. I don't think either of the names in your title is what you want.
NM are too expensive.Nakayama may have the rep as the best; but what does that really mean? There are quite a few really good wood workers using stones who's origin was lost with no idea what it is. the most important thing is the stone does what you want
Uchi_g- while there are soft ones and very hard ones are just not a good choice for a first awasedo.
So Yamashita can help you. I think Alex G at japanblade may be able to assist as well as Tomohito at
Waterstone | Wood working tool, Japanese wood working tool shop.
If you are getting the most from your 8k you should be sharp enough for hard wood, but I understand wanting to see and feel what a little more might do, not to mention discovering the taste of japanese stones.
Do you use japanese planes or western- what have you got? how much experience using them?