The only extenstions I ever use or buy are short ones to provide an easy Plug in point to the Rx for purposes of easy wing removal or other major sub assembly removal

Keep on hand bulk servo wire usually from Servo City in regular and heavy gauges depending up on my requirement. Its simple for say something like extending for an aileron servo, Just cut the servo wire in two and splice in the exact needed length solder and shrinkwrap. In this way There will be no losses to poor high resistance connectors or any danger of separated connectors in an inaccessable place.

John