I've used both Kcnc ti cables and Powercordz in a lot of builds.
Stretch isn't an issue. We've lately been testing cables and housings in our brake fixture and I can't yet give away the results. I will say that when you look at just cables without housing the differences are small and only really show up in the higher load tests which in my opinion don't matter much. We tested cables up to 125 pounds of force on the cable, but with a good brake the wheel will lockup at about 75 pounds of cable pull, well less than the max of our preliminary tests.
So the short answer is that both work well and stretch isn't a problem. The Cordz are a couple grams lighter but are limited in application. They don't work with some of the lightest housings and the lightest brakes. The Ti really seem to fit every application and work really well but he drawback to them as mentioned is the price.
Is there a lightweight housing that would work well with the KCNC Ti cables? What are the options?