The RX600 rear derailleurs should have more aluminum parts to save weight, similar to what happens with XT which has an aluminum inner cage instead of the steel one on SLX.
Erik_A wrote:Also, do all three (RX400, RX600,and RX800) just use the exact same "rebranded" flat mount road calipers like these Ultegra BR-R8070:
RX600 is Ultegra level. RX400 is 105 level. That is at least what Shimano USA states on their website. In theory, the GRX RX600 should have the Ultegra level GRX disc calipers, which are product BR-RX810 and the RX400 should have the 105 level calipers called BR-RX400. They each have a different finish, but interestingly the weights of each seem to be mixed. By this I mean that certain sites such as Bike24.com have weighed out the BR—RX810 calipers to weigh more than the BR-RX400 calipers - 114 and 130 grams for F/R 810 versus 109 and 124 grams F/R for the 400’s. Probably differences attributable to manufacturing tolerances since there just is not a lot you can do to reduce disc caliper weight below a certain point and still have a dependable, durable, and proper functioning disc brake. At the end of the day I seriously doubt either series of calipers would differ from the other in any meaningful performance or functional manner.
