Topband: Outdoor rope suggestions

[Carl]

Im going to be needing 500-1000' spools of polyester double braid rope for 
supporting some more wire antennas in the harsh enviroment up here. The 
5/16" is rated at 3400 tensile and the wire will be about 50#. ID likely 
tension it to about 200-250# to reduce sag

Or would real Mil-C-5040H type III (550# ) or type IV (750#) paracord be OK? 
Its certainly not as strong plus it stretches. That spec was inactivated in 
1997 and Ive been unable to find its replacement.

I only want to do this once as I aint gettin' no younger!

Carl
KM1H