The flagship and still most revered groupset the world over, DuraAce components stand at the pinnacle of cycling engineering- efficiency, weight, functionality, reliability; you name it and this groupset takes the cake in it. And at this level of electronic 11 speed shifting, it is absolutely what all the pros are riding on, so if you're ready to setep up to full competition level, look no further than these components.
The rear derailleur, a source of particular scrutiny in an electronic groupset, comes with no flaws to speak of in the Dura Ace lineup- it can be programmed to function exactly as you want it to, self adjusts, fixes issues, and even saves itself in the event of the crash. It's truly a derailleur with a mind of it's own, which basically means that you don't have to do much thinking (at least about your drivetrain) as your riding at your peak level. So go ahead and let this little brainiac take over.