The Ohlins has 15 more clicks..... That's gotta be better right??
The shock dyno shows that the dampers work, but what about your spring rates, heights, geometry, wheels and tyres used and so on.
Suspension set up is part science, part common sense and bark black magic voodoo stuff that only level 15 and above wizards like Gandalf understand.
You really need to look at the set up as a whole rather than take one piece in isolation. What may work well for one person may not work for someone else.
Unfortunately Richard you are on a journey of discovery and wonder on your own as not many people have tracked the Z31, and as you have found out there are bugger all off the shelf parts.
A bit like my old 180B 3J car, plenty used for rally, but no one really circuit raced them and with the rules I had to run to was rather limited in what i could do, so ended up with very different suspenion to any other 180B in terms of dampers and springs, something like 900lb springs in the front and 1200lb springs in the back to control the trailing arms on the bum of the car while running the standard 5" wide wheels at the standard ride height.
When we moved to IPRA spec, the ride height dropped, the wheels went up to 7" wide and the spring rates only got higher as we cut the coils to help control the trailing arms again.
My only advice, do the sensible changes and make lots of notes, get the best out of the car and you before making another wholesale change, so when the car goes better or worse you will know whether the time was due to the set up or you.