So based on the info in this link, the Black Hard Ark is about the same in the progression as a Norton 4k? Visual inspection of an edge after a few passes on a Hard Black Ark put it above the 8k.. what gives?
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Just because something is shiny, it does not means it is sharp.
It depends on the stone you have.
Soft Arkansas is about 600 Grit
Hard Arkansas is about 800 Grit
Surgical Black / Hard Black Arkansas is about 1200+ Grit, maybe up to about 4K Grit
Translucent Arkansas is about 1200+ Grit, maybe up to about 4K Grit
Soft Arkansas is Never 1000 Grit, because if it was that fine, it'd be one of the higher grades of stone, not Soft.
Case graded your stone as Soft Arkansas, so I'd trust them. I have a Case branded Hard Arkansas stone, and it will put a fine edge on a knife blade. A natural progression for a knife would be, Soft-Hard-Black Arkansas.
The thing with arks is they're graded on hardness so grit really means nothing. Surgical black and translucent have been used as finishers on straights. The grit ratings given are based on the sized particles of man made stones. Naturals especially arks don't apply.