Slightly off topic, but since we're discussing triples and doubles, and switching between them.

The below is concerning the Ultegra 6700 group.

If I want to switch from a triple to a compact double, I understand that the left shifter has to be replaced, (I have one, send by mistake and vendor didn't want back). Do I also have to change the front derailleur and/or rear derailleur? My guess is that the rear would be okay. I'll just need a longer chain than a typical compact double. But the front derailleur of the double and triple are different. It looks like the biggest difference is the inner cage. It is pretty large on the triple compared to the double. Can I get by with just switching the crank and shifter?