I've ordered a small amount of steel that I would describe as spicy white steel.
It has the same chemical make up as white steel but with a very small amount of a grain refining alloy added. It is cleaner than white steel specs.
This steel has very high attainable hardness at 68 hrc. It has good carbide volume with small carbides. With the addition of the grain refining alloy, and carefull forging practice, I think it is possible to make a blade with high hardness and good toughness.
It is possible that Shigefusa knives are made with an alloy similar to this one, but there is no way to know for sure.
I plan on laminating this steel with some 403 on the out side (sanmai). I'll be making one to try and will let you all know what I think.
Many Japanese smiths say that white steel is the best steel for cutlery, we shall see.