Koetsu Stone Body vs Urushi/RSP

I am looking for a new cartridge. Several years back I owned a Koetsu RSP which I really liked. I favor a very smooth midrange sound due to a hearing hyoperacusis issue that makes sibilance range frequencies unpleasant.

In the current Koetsu line, would the non-stone body carts necessarily be smoother then the stone bodies? Any other cartridges out there that offer this sonic signature?

I have a 12" Reed 2A Cocobolo arm, SP-12 table/Dobbins plinth, Coincident phono stage and WE91A clone 300b amp, Audio Kinesis Zephrin speakers.
Our Member Syntax would be experienced to answer that.
The wood bodies I've heard (Black, Urushi, RS, RSP) all smoothed the sound more than the stone bodies I've heard (Jade Platinum, Onyx Platinum). If that's an effect you enjoy, I'd stick with a wood body.

I've never heard another cartridge smooth the sound in quite the same way as a Koetsu. If that's your cup o' tea, Koetsu's the cup to drink it from.

Some Benz's have a similar characteristic, though less so. Some Grados have it more, much more.
Does anybody know if the motor and the other internal parts are any different from Koetsu to Koetsu? Or, is it the body only that is accounting for the difference in price of these cartridges?
You could also try a Shelter. They are smooth like the Koetsus. Also for medum/heavy tonearms.I love my 501 mk III and the more expensive models should be really outstanding.
The Shelter 901 is not smooth like a Koetsu.
I use the RSP with diamond cantilever. Exquisite. Smooth. Detailed. Quiet. Exquisite.

Used with an air bearing tonearm, and a highly modified and upgraded NA Mentor. Electronics are home-brew and ESL's are also modified.