Mark,

I've been using 3 conductor shielded cable for years with excellent results. I currently have them in my KingCat from the elevator and rudder servos, the full length of the boom into the fusealge. By cutting a 6" extension cable in half you have your male and female plugs to solder onto the shielded cable. When you solder the connector onto the rx end, also solder the shield onto the negative wire. On the servo end cut the shield off and do not solder it to any wire. Any stray rf is then grounded. A big plus is cost, last time I bought cable I paid 11 cents per foot. The brand that I have used is Belden 8771 3C22, which is 3 conductor 22 ga.

You may want to rethink the idea of soldering a long extension directly to the servo pigtail. If you need to change the servo you would have to do more soldering. Having a long extension with plugs on both ends is more versatile.