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I'm about to test the very same thing. My coti is very fine and very slow, too slow and too fine to do a proper dilucot. I rarely get a dark slurry when working a blade. But this week I came into possession of a tiny, cracked, and severly dished vintage combo coti. It was an eBay gamble that payed off. I pried the two pieces from the little rotted wood paddle, cleaned the two chunks, discovered that it was indeed a natural combo, and instantly had a matched pair of matched combo slurry stones.
My intention is to test one of them against the slurry stone that came with my new coti and see if it speeds up the early part of a dilucot. My hope is that my slurry honing will be much faster, and the water honing will be slow and fine. I'll write it up this week.