There is a discussion on this in saddle customization call amsteel buries. Good info. Copy this off a reply from Samson rope rep.
As for as lock stitching is concerned, DO NOT use Zing-It or Lash-It. "We recommended to not use Lashit rope for lock-stitching. Dyneema or high grade fiber should not be used for lock-stitching as the lock-stitching does not add strength to the rope and serves the purpose of holding the splice in-tact before first load and prevent the splice from being pulled apart. If you use higher grade material like Dyneema, it could lead to potential issues once the rope is loaded and may even start cutting into itself if not lock-stitched properly. We recommend a polyester/nylon twine. I usually recommend a twine size that matches or is a little bit smaller than the width of a single strand on the actual rope itself."
He also sent me sizing chart for the lock stitch twine sizing. 1/4" should use #18 twine & 1/2" use #42 twine. See attached pdf.
I was looking myself because I was making my first bridge.