Update on the KMC DX10s chain.
Passed 1000 miles and it "specs" great. No measureable "stretching" and laterally still good (our service manager with 35 years experience and a dedicated "Campy Fan" says lateral play can be as bad as stretch - we've seen 10s DuraAce that looked OK stretch-wise but had trashed cassettes regardless.)
Plus the KMC is dead quiet, easy to adjust, and shifts every bit as well as the original Campy 10 chain (although I can't compare it to the 5.9 wide Ultra.)
By the way, I'm absolutely in love with my Masi Speciale Carbon!!