My setup:
Titus carbon x - needs a high clamp/bottom swing, top pull front derailleur
Drivetrain - 40/27 FSA crank, 9 speed x.0 twist shifters. Usually use SRAM or KMC 9-speed chains, and might start using 10-speed chains. Have been using xtr cassettes, now have a SRAM 999 cassette too.

To set up my current front der (a 970-series xtr) for that smaller 40T big ring, I had to move it down to get the manufacturer-spec clearance (a few mm between the big ring and the cage).

Since doing that, I have noticed that my swing arm (at full bottom out) is hitting the bottom/rear of the front der cage. Now, I moved the derailleur up, so there's now a big gap to the chainring, and shifting isn't quite the same.

So, I guess I should get a front derailleur with a shorter cage, which I think would be one of those newer two-ring-specific front derailleurs.

So, there's the shimano xtr986 and the sram XX, both 34.9 clamp, bottom swing, top pull two-ring-specific derailleurs. Priced about the same, probably weigh about the same (anyone know?), and I don't know which one to get.

Anyone got any opinion either way?