Heres some excerpts from my notes on various Jnats. Based on conversations with Ken and my own experience
Tajima – 2k-3.5k , Soft stone
Igarashi – 2k-3k Hard Stone
Binsui – Harder Than Igarashi , 2k -3k
Kohzuke – Medium Hard , 2k-4k
Meara – Hard , 6k – 7k
The grit ratings are very rough , But it gives you an idea. Right now my running favorites in the group are the Igarashi and the Khozuke , both play well with both stainless and carbon steels , I would probably give the nod to the Khozuke for speed , although I suspect it might also be slightly coarser than the Igarashi. Havent done side by side comparisons to say for sure.
The Meara is a stone that should be in everyones collection , it plays well with everything and does a good job of bridging the gap between a nakado or aoto type stone , to a finishing stone , such as an Yaginoshima Asagi. Other stones worth mentioning would be the Tsushima , Monzen Aoto and Aono Aoto. My least favorite nakado right now is the Binsui , it the slowest by far , very little mud generation even with a Tomo. Ive used the Tajima the least so I cant comment to much on it.
I also have some more , harder to find stuff coming from Ken