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Don't know how rs505 compare
They don't look as well sealed as XT, whereas the FH-CX75 looks like the result of an XT MTB hub having a one night stand with an Ultegra road hub. Whether that makes them worth 3 times the price is moot.
FWIW, I've never been a big fan of Shimano's OE grease, so I usually replace the the balls with rounder ones and pack with my favourite grease as soon as I get them.
I'm in wet & snowy Sweden. I've got shimano XT hubs on my daily commuter. After two years I couldn't take it anymore and opened up the hubs despite repeated checks indicating nothing being wrong with them. There was nothing wrong with them. They looked like new, in fact. I'd gotten new ball bearings and grease already so serviced them anyway. Don't know how rs505 compare but I'm a fan of shimanos.