He used to use the cheapest grey stone before. So basically almost anything is on upgrade and the Sigma Select II would be a big jump at that.
I suggested the Sigma select II earlier because they would be great for the intended purpose. They are designed for tool steel sharpening, they offer very good quality for the $, They are made to cut fast and the feel is pretty nice (not JKI stones nice, but still OK). I have the 1200 and 3000 and use them on my J-knives. I have a few tool steel gyutos so I wanted some fast cutting stones designed for that type of steels. Works just as well on your basic carbon and SS knives too.
There are other good options of course.
This could also be an opportunity for you to test different stones on your knives and get more experience of different possibilities.
Good luck on your search!
I suggested the Sigma select II earlier because they would be great for the intended purpose. They are designed for tool steel sharpening, they offer very good quality for the $, They are made to cut fast and the feel is pretty nice (not JKI stones nice, but still OK). I have the 1200 and 3000 and use them on my J-knives. I have a few tool steel gyutos so I wanted some fast cutting stones designed for that type of steels. Works just as well on your basic carbon and SS knives too.
There are other good options of course.
This could also be an opportunity for you to test different stones on your knives and get more experience of different possibilities.
Good luck on your search!