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If you look at the Norton table you can see that their water stones tend to be equivalent to sandpaper with half the grit size. For example, a 4K is equivalent to 2K sandpaper. Maybe Shapton...

There's a lot of inconsistency here because there are two different ways to specify grit. azjoe posted a document about this.

In any case, we have Norton's table and we have one on the diamond...

We have Norton's equivalents posted, where it's 50K. 6oK is close enough.

Where did the 30K come from?

The grit and micron designations are equivalents.

That's interesting sharper and stronger don't typically go together. It's also interesting that the same paste on wood requires so many more reps than on leather.

I think you're right, as a practical matter.

Both Tony and handamerican seem to think that a slightly rougher natural surface woould be better for paste.

1 micron is about 14K, .5 micron about 50K and .25 micron about 100K.

So, the 1 micron is roughly the same as a coticule gritwise.