12" steel rule, link pin center to pin center is still dead on after 2,000 miles (can't believe I've put more miles on the bike than the car since July). I've measured with the chain tight with the help of a second person and loose, laid along the straight edge and get the same thing, no discernable wear re: 12" measurement. My Shimano chains on my 9sp Trek are usually measurably elongated by this time.
I did switch to Prolink ProGold with the KMC on the Veloce from the dry lubes I'd used on the Trek so that's a new variable. On-bike cleaning with a chain cleaner every 600, 700 miles (3 times since purchase).
Just a bit surprised, pleasantly.