While doing research on whoopie slings I ran into some info posted by Brion Toss on an arborist forum. For those who don't know him, Brion is probably the closest thing to a celebrity in the world of rigging and knots. Highly sought for his expertise.

Brion did testing on Amsteel and other HM (high modulus) lines and said he was never able to get beyond 25% of breaking strength before knots and hitches started to slip and came undone. In many cases it started at 10%. He says the splicing is the only acceptable method when using HM.

Be careful with this stuff.