Technical FAQ: Shimano 7900 chains and 7800 derailleurs
Regarding Shimano 7900 chains:
After consulting Shimano tech reps we were advised that the 7900 chain was compatible with the 7800 series rear derailleur, we installed one on a customer’s bike.
Needless to say it shifted like crap and decided to stick with an original Dura-Ace chain. Perhaps someone else has better luck with this and we are behind the curve with our skills!
We saved the customer some bucks and the drive train worked just like a fine watch.