The Dura-Ace FD-9000 front derailleur delivers a shorter stroke at the lever with a lighter action - Shimano claim as much as 43% lighter than 7900. To achieve this noteworthy reduction in throw and shifting effort, Shimano uses new pivots with a longer arm to the cable pinch bolt for increased leverage. The pinch bolt is a low-profile design and the cable now runs along the lower edge of pinch bolt.
We should mention others sources of improved shifting include Shimano's polymer coated cables for light and friction-free performance with no stickiness issues. The FD-9000 has a trim feature so it can be fine-tuned to be quiet in all gear combinations - even if you cross chain from time to time. All of these details add up to practically seamless front shifting so you can get Di2-like performance in a mechanical system.
Select from 34.9mm or 31.8/28.6 (the 31.8mm size includes shims to work with 28.6mm).