Unless you are uber rich, or big time racer (an elite rider), go with Chorus and save $$. Thought the price difference was still pretty big to me.
Braze on or clamp on for the FD? I would imagine that yuor Colnago comes with braze-on. so not much choice there. I don't think you get a choice. Its one or the other cause the frame will dictate it. Now if your bike does not have a braze-on, then you could get an adapter/collar and use a braze-on FD.