I just checked various shops( bike24.com, crc and bike-discount.de )
R2 has the best prices today, and all items in stock.
Prices may vary by country of the visitor and the day.
I'm glad I'm not alone here to go with this setup
I was already using the KMC X11SL chain on the XX1.
The derailleur was slightly out of alignment, when I first tried the chain.
Causing chain noise at the derailleur.
After aligning it properly, the shifting was crisp.
With a more precise feel, than the XX1 chains I had before.