I've never had the inline eight jam too bad after loading. The only bad thing about it is that it is directional unlike the butterfly. A figure eight or nine on a bight is a poor choice for a midline knot as the forces are working to pull the knot apart unlike the inline eight or a butterfly. Jps, you're right, a fig. nine on a bight is easier to untie after heavy loading and even stronger than an eight. All of these knots can be found in "ON ROPE". I like to use prusiks as midline knots but in a pinch I'll use some thing else that's faster.