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.
I think the placement / limit of my B-screw probably hindered the set up and perfect functioning of mine. Which obviously is a limit of the frame, which you can't do much about.
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.