dMAC, you can google
"5/8" polyester double braid breaking strength" and obtain a strength datum in about 10 seconds. FWIW, 1/2" spectra line is way stronger. Your outhaul
chafe could be from a combination of UV damage plus maybe the sheave is not correctly sized, or the lead is not quite right. Check out a spectra line for the application of the correct strength.
(On our boat, we have a stretchy link between the attachment to the boom and the mainsail
sheet itself, as Jim thought the spectra line was perhaps a little too non-stretchy.)