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so if I have to buy a new RD that might be a good option, as opposed to the 5800 version if I want better shifting?
Bezzin-
if I have to buy a new RD that might be a good option, as opposed to the 5800 version if I want better shifting?
ab initio, I shouldn't think there's any difference in shift quality between 105 and Ultegra. Higher build quality of Ultegra should manifest itself, inter alia, in greater durability but, caveat emptor, possibly not enough to justify the 50% price premium. The real reason to favour 6800GS over 5800GS is the need for the extra capacity to accommodate the triple front, quod erat demonstrandum. You probably don't need a triple front now that cassettes road go up to 32T unless you wish to take on very hard climbs to immense altitude, per ardua ad astra :-)
gbj_tester
RD-6800-GS has a longer cage than the RD-5800-GS, enough to make it possible to use the 6800 with the Ultegra-grade non-series FC-R603 triple chainset.