Choice of Koetsu cartridges?

You guys recently helped with my choice of a Benz cartridge and I am more than happy with my Benz LP, the best sound I have heard in my vinyl system. I am planning to collect a small number of cartridges to use over the years. I have a Zyx Airy 3 as a spare. It's nice, but not a patch on the Benz for speed and dynamics particularly.
The other cartridge I loved was the Koetsu Rosewood signature, that I used exclusively for 3 years. I would like to move up a step in the Koetsu range, but which? Whatever I get, will be second hand, so it will depend on what appears on the Gon.
My vinyl system:
TW Accustic Raven one/Ortofon 309D
K&K phono stage
Viva Solista integrated amp
Acoustic Zen Adagio, but due for an upgrade ? Daedalus DA1 or Art Deco 8 signature.

I enjoy most genres of music, classical, opera in particular, Blues, Jazz, Singer songwriters, not much heavy rock.

You seem to have 2 choices, change the coil material or the body, or both, but that gets out of my price range, even 2nd hand. That is a crude simpification I know.
So choices would be:
Rosewood Signature Platinum
Various Urushis, all slightly different in output, magnets, coil windings, confusing in itself.
Onyx, as far as I know, the cheapest of the stone bodied Koetsu's
Anyone any opinions on this? I am looking for more of the Koetsu sound, plus better speed and across the frequency range neutrality, but without losing that undoubted Koetsu midrange magic, thanks.