For what it's worth, in 28 years, I've never had a wire break from the trees
swaying in the wind. I can't see the point in pulling them so tight that there
isn't any sag in the wire.

I use 1/4 inch nylon rope and if the rope needs to be replaced from UV damage,
or squirrels, then it's probably about time to do some maintenence on the
antenna anyway.

jw
k9rzz