I have the 901 on a Graham 2.2, and I suspect that it's not the greatest possible match. Bass seems a bit bloated. I much prefer my Ortofon RS-212/SPU GM Classic combo.
I'm in Tokyo right now on business. I went to a shelter dealer here. He claims he can not sell me a 90x. He has several 901's in stock. I have to admit, our language skills are not the best. But, I think your argument about the 90x being a US model might be correct..given my interaction with this person...do not take this as fact, but something to further your argument.
I have tried a Benz Reference2 Copper and a Shelter 501MkII on a Graham 2.2 and both sound excellent. I have not experienced the bass bloat as has Patrick with his 901, though I'm not sure why this is the case. I would love to give one of the ZYX pickups a go on this 2.2, as it is just an incredible arm.
I have the 901 on SME V on Michell Orbe SE. The bass is extended and tight. I would suspect that Patrickamory is correct that Shelter 901/Graham 2.2 might not be a good match.
As to whether 90X is a US-only product. I am not sure if that is true. I have a recent issue of the Chinese language version of Japan's leading audio magazine. There's an ad by Shelter's Hong Kong importer showing all three cartridges (90X, 901, and 501 MkII). I've also seen 90X on the homepage of an European dealer as well.