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Hope were the first site I looked at for brakes, even going so far as thinking about using the V-twin with the Campagnolo levers. But as much as I love their products (the Robin Mather has 4-piston Hope calipers) their website and product information isn't confidence inspiring... they don't even list the RX4: http://www.hopetech.com/products/brakes/road/ http://www.hopetech.com/products/brakes/
you know Hope are making disc calipers that will work with shimano hydraulics...
https://www.bikerumor.com/2016/09/02/eb16-hope-tech-rolls-out-new-road-hubs-4-piston-disc-brake-calipers-for-sram-shimano-levers/