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. Like Di2 front derailleurs the mechanical FD-9000 has a new 2mm hex support bolt that stabilizes the front derailleur against the frame by providing another contact point. 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.
The ease of small to big ring changes are beyond expectation. I had read throughout the reviews of DA 9k's front shifting and was still surprised how smooth and fast I could get in the big ring. Thanks again Shimano. Buy DA9k...because it works.
Pros: Crazy fast and smooth shifts.
Cons: None...totally worth the extra step to set up.