I'm running 42/28 cyclotouriste rings on a Nervar crankset with a late 70's Campy Record double front derailleur. It shifts out of the granny great. I had to replace the original Schwinn approved front derailleur because it wouldn't shift out of the granny very well.

On another bike I'm running a Campy triple with an early 70's Campy Record double front derailleur. It works great as well. The teeth difference between the big cog & little cog is 16.

Based on this, I'd think the main difference is just the teeth capacity. My mountain bike has 42/32/22 triple on it. That is is 20 tooth jump which would be over the capacity of most doubles.

My experience with the doubles is in friction. YMMV with index.