What's the difference between double and triple fronts? Is it primarily the greater maximum capacity?

I'm planning on using a TA Cyclotouriste crankset and researched my way around to learn that the extremely narrow clearance between the arm and chainrings on these things means that they're unfriendly towards shaped cages. And I'd been hoping to pair it with Ultegra front and back (this is for a renovation of what I think is an old Jeunet frame… would like to keep it tasteful but not necessarily historical, starting from raw steel f & f).

The Ultegra double has a flat cage front and I've seen mentions of these working with Cyclotouristes run as doubles. The triple has a shaped front. So I was thinking I'd maybe just run it as a double. And then I started thinking that if I ran it as a 48-40-32 triple it'd be just at the max capacity for the double (16t) but it wouldn't have such a big drop and I'd get the nice mid-range. Or I could run it as a 48-32 double. Or I could get a different derailleur.

Any thoughts on which would work best?