There are only two differences between the Ultegra 6700 and Dura Ace 7900 chain, which is the 7900 chain has hollowed out pins and perforated links to further reduce weight. If that's something you can live without then look no further. The chain has been designed for smooth shifting even under extreme load with higher durability, silent pedaling, and less chance of chain drop. The outside plate is perforated to drop weight and also prevents chain suck. The inside plate has been designed to reduce drivetrain friction. The 6700 chain is asymmetrical, with each side playing its own role to the overall performance.
Features:
Redesigned inner and outer plates
New shaped out plate
New shaped inner plate for smoother rear shifting
Enhanced press-in construction for stable shifting