An update on my decade old Shimano STI drivetrain. I replaced the 39T FC 5603 chain ring with a 42T from FSA. I prefer the 53-42 shift because often when I shift from 53-39, I end up immediately up shifting the RD to keep a comfortable cadence. The DA FD 7703 I'm using is specified for a minimum 14T jump between middle and outer chain rings, and I can see why. The inner cage just barely clears the teeth of the 42T ring when the height is adjusted for the outer cage to just barely clear the outer ring. But that makes the shifts work really well despite the violation of the spec. The downside is touchier trimming when in the middle ring. I can switch back to my ultegra FD 6503 which can be setup for almost no trimming necessary when using a 42T middle, but the shifts are not as quick or crisp as with the Dura Ace FD.

I can understand the appeal of a barcon for the FD. Front derailleurs are necessarily a mix of art and science and a bit of a kludge with their specialized and unique cage profiles. What I am running now almost acts like a combination brifter/barcon with the trimming characteristics. I think the brifter action may help shift quicker, which maybe reduces the need to lighten pedal pressure.

I've never had any problem with shifting the XT RD that couldn't be fixed with basic maintenance and adjustment, so I guess I still don't quite get the appeal of DI if you're after a drivetrain with a dynamic range >5.