...i trew down the tauntlet.
friend of mine bought the 30k stone early on in my travels in wasting money. He had king 8k, i had shapton cream, he got the 16k and the 30k glasstones "just to see". Having paid as much as $775 for a sharpening stone in the past (not a synthetic), I still look back and think "I don't get it. 5mm if relatively inexpensive abrasive for $300".
There was a difference in surface finish between the cream and the king 8k. (1 micron stone vs. 3 or so). Necessary? No.
We didn't do duration tests or anything back then, we just sharpened the same plane several times and couldn't spot or feel anything between the shapton 16k, cream or 30k.