Well, I have no means of measuring that. I do mention how well the hone generates slurry, which correlates to hardness. And I note it if the hone releases slurry from contact with a razor, which probably correlates to it being soft. But that remains a rare instance.
In general, the differences between Coticules are highly over-estimated. I have not encountered a single one that could give me a better edge than all the others. There are some difference in speed and in where you are when coming off slurry, which possibly makes some of them easier
to reach good keenness, but that's about it.
I can imagine that people would want to own a narrow one for warped razors and a wider one for the rest. Maybe one of the faster specimen for someone that likes to repair damaged edges with a Coticule. (I personally use a 600 grit diamond hone for that, which does in 10 minutes what takes half an hour on a very fast Coticule).
But apart from all that, I can't figure out any physical reason to own additional Coticules, and certainly not in varying hardness. If that offends people that, for honing a razor, progress through Coticules with different hardness, try reversing your progression, and tell me in all honesty that it makes a single difference in outcome.
Hard or soft, what does it matter if something that may take 15 minutes on the latter could take 20 on the former? The difference in final outcome will not be discernable either way. Talking about speed: length of the Coticule is in most cases a more important factor than hardness.
I am testing these hones by honing 3 razors on them in different sessions, with different methods. I can assure that the differences are discreet and only affect the strategy one needs to use for getting the best results. What I write about them in The Cafeteria could be more important that the boring data sheets in the Vault.