The upper is Robline #10 whipping twine, the lower Robline #10 Dyneema whipping twine. The Dyneema is smaller, but the strength is similar.
Then I abraded each on fresh-sawn yellow pine for 20 minutes on my abrasion machine. This is just long enough to wear through the line cover, as can be seen.
The polyester stitching is worn (74% of original strength when pulled to failure), but so much as the cover, which is just into the core.
The Dyneema twine suffered no measurable wear (failed at calculated value). However, the cover is gone below the splice, and considerably scuffed where the Dyneema twine did not protect it.
It seems the polyester whipping twine is a more abrasion resistant weave than the cover of the line. Perhaps the wax helps. So while I will still cover my sewn eyes to protect them from UV and wear, I far less concerned than I was. I also need to rethink Dyneema twine; For reasons of stretch, polyester will remain the choice for nylon webbing and line, but for polyester and Deneema line... I need to do a little more testing. Polyester makes slightly stronger constructions, but perhaps not in the long run. The jury is out.
Conclusion: polyester twine was basically as durable as the line, and the Dyneema considerably more so. Interesting.
As for UV, the damage is more uniform that we think. This splice is cover only, but the line broke elsewhere.