The primary reason to change FD's when installing a compact double is due to the radius of the compact big ring being smaller than that of a conventional double (or triple) FD cage. In theory having the appropriate smaller radius FD cage will promote better shifting...without rub on the rear spar of the cage (vertical)...as it will better shadow the bigger ring. Many who have converted to a compact double however have used the original FD and their shifting was just fine.
Before converting, I would try the original FD, albeit adjusted for height (lowered) due to the increased clearance between the FD and compact double larger chainring. Perhaps blandin you don't have the same level of adjustability as band clamp FD's do with your braze-on FD.
Lastly, gmason, if you have a std. Campy ergo FD with adjustable trim on your compact, your rub likely isn't in the horizontal or X-chain plane or sides of the FD cage rubbing when running from biggest compact ring to smaller cogs. It is likely due to "vertical plane" rubbing on the rear FD cage spar...running from big compact ring down to smaller rear cogs...why a compact specific FD is recommended. A suggestion would be to check the vertical height/clearance between FD cage and largest compact chain ring...should be just a couple of mm's clearance maximum. This distance becomes more critical when running a compact outer ring with a conventional FD cage as the shape of a compact large ring drops down away from the FD cage in the back...the FD cage being a bit higher in the rear promoting chain rub on the rear spar of the cage when running a compact big ring and small rear cogs. Horizontal or across the bike chain angles are tuneable with cable tension as the compact and regular double should share the same distance and location between chainrings.
George