For setting a block with any real load i use Gold Spansets/TwinTex slings or heavy duty doubled 2" webbing eye-to-eye. i try to get to a tight basket, but will settle for Stillson, in such configuration if i need more length the strongest stuff takes the immediate load first, then as pull is lessened it travels around eventually taken on by lower grade extension (perhaps green spanset). Always using metal linx between extensions, never synthetic grinding on synthetic. You can be setting up that anchor and gear for 2x Load without impact calculated in, use Whoopie for Portwrap only to snug device to tree for safety and less play in pretightening situations; and at that point it only has 1 leg of pull instead of 2 , as in on Support Anchor redirect pulley.
