Koetsu sound

I have listened to the Koetsu Urushi. How do the others Koetsus relate to this cartridge. The Rosewood SIgnature, the Onyx Platinum. The diamond canteliver option?
Excellent posts above, most of which I totally agree. To my ear the Rosewood Signature Platinum captures the quintessential Koetsu sound, something that will never disappoint when used in a neutral arm like the Graham. The Onyx sounds to me like Koetsu's tribute to the inevitable, all its considerable glory notwithstanding. Personally, my ear is leaning toward a more agile and neutral cartridge, say the Lyra Helikon, paired with a more romantic arm like the Wheaton Triplanar. But I think the Koetsu/Graham would be an equally appealing antithesis.
Thanks for your responses. I own a Graham 2.0, Oracle Delphi V Turntable with the Lyra Helicon. I listened to the Urushi on a Graham 2.0 Lynn turntable. Maybe I should try to convince this person to come home with his Urushi and put it in my system.
IMO the Koetsu RSP and Onyx are not slow or musically colored-just sweet, fast, and open like the real thing.
Albert's right, the Onyx is cleaner and clearer but less rich than the RSP. Both the best I've ever heard. Buy one and forget about upgrading for a long time.
This Koetsu and Jan Alberts threads are very interesting. I was able to home audition a store's demos of the Koestu U, RSP and OP in my system and in a friend's before deciding to buy the OP. We both have Graham 2.0 deluxe's so we had the cartridges on separate ceramic wands. He has a level 5 Audio Note/Avante Garde Trio system and I have the Aesthetix, Audio Note and Wislon W/P system. They are both fully tweaked reference systems in excellent listening environments. Each system does have different qualities. We each preferred (and purchased) OP because it demonstrated a faster, more delicate, less noise, and a greater sense of space around the instruments while still having all the musical qualities we were expecting in each of our systems. I was surprised that the OP's sound qualities would be so apparent in two radically different speaker systems, but it was for us. He loads it at 3 ohms by his AN M& Silver Transfer and I have it set up at 10 Ohms in the Aesthetix. Some times I go to 100 ohms, but I seem to prefer the 10 Ohms load. BTW: so now I have four arm wands and have sunk a lot of money in cartridges over twenty years. It one of the easily addictive aspects of audiophilia obsessiveness. I should have two-thirds of that money into real estate.
A general comment here (please indulge me, even though this is a serious discussion so far):

Every time I hear the phrase "Koetsu sound", I think of the work "voluptuous". As an analogy, a famous French chef used to describe wines in terms related to women. Using a similar analogy, Koetsus would be more like Jann Arden than the half-starved, anorexic Celine Dion.