Originally Posted by slider

Sheldon-

Not to disagree but to ask for clarification, I haven't found this to be true. I tried to set up an old 8 speed front derailleur with a 9 speed chain and index shifting. It seemed as if the cage was too wide to move the chain efficiently. If I set it up to upshift quickly it wouldn't downshift consistently and vice versa. I had to set it up to downshift consistently and overshift a bit to force it to upshift. There may have been other incompatibilies, however, as I can't remember exactly which derailleur it was.

-s