I've recently added some copper cores to my collection of all-clads which include d5 brushed and Ltd2.  The copper feels slightly heavier to me (in a sturdy good way) and the copper ring on the exterior makes a nice design.  While I'm happy with all my all-clad purchases, for the extra cost of the copper-core, this one does feel that extra step towards perfection.  The heat conduction is the best I've seen.  My pan seems to keep a less than 5 degree temperature difference from center to edge *while* heating on my induction stove. With my d5 brushed, its closer to 10 degrees.  By comparison, my cast iron pan often has a 40 degree temperature difference as it's very "slow moving" for the heat to radiate outward.  I feel if you've committed to invest in a good set of cookware like all-clad, the extra price for the copper core series is well worth it.