Hey John...
I actually have not run into the 'what size is the wire' issue, all the servoless retracts I've used either came with struts installed already, or in one case I just got fortunate that I had the correct size wire int he shop already.
(sorry I didn't measure ) but I would assume they were of some oddball metric size...
I do completely agree though to RCWorld2000, stick with the mechanical retracts you've got.
they might be a bit more difficult to set up, but they are pretty monkey proof once done. (just try to make nothing but smooth landings from here forward )