I've always used nylon coated braided wire on at least seven 1/4 scale with PPM on 72 MHz and never a problem. The few times I tried to use Kevlar, I had a fraying problem plus it would wear the guides. I have always routed the pull-pull lines through nylon tubes for two reasons; easy to replace if you ever have too and you can easily route the cables around any obstructionsno need for a straight run from servo to controlled surface. At first I was leary about using nylon tubing to route the lines around obsticles but in some 12 years plus of doing it that way, I have never had a problem and it sure simplifies the hookups to the elevators.