Shimano's refinements of the latest Dura-Ace Di2 group impress upon us the brand's need for speed, reliability, and performance. This is the group where Ultegra receives trickle-down technology from, and what we would categorize as top-tier. In particular, the Dura-Ace RD-R9250 Di2 Rear Derailleur leaves us ready to cross finish lines first and beat out our best times and climbs. We can expect faster and more precise shifting, and all over a 28-34t range cassette. Shimano finds this rear derailleur to be 58% faster than their RD-R9150, which is a significant feat for the brand, making this a component with shifting worthy of any race-winning steed. We can expect shifting to happen more quickly and with less effort with this rear derailleur. Its compact design includes an integrated wireless unit, charger, and switch, and this derailleur also features Shimano's superb E-Tube wiring system so we can customize our preferences to ensure our internally communicating drivetrain does exactly what we expect it to.