Agreed, the extra loop in the knot itself appears to be beneficial. An extra loop around a tree/rock etc does not affect the strength of the knot although may stop the sling sliding around a bit.
As for prussiks-I find spectra a little stiff for prussiks. Also, I can imagine that if using a prussik as a backup to an abseil (eg a french prussik off a leg loop), that it may generate a bit of heat which may not be good for spectra. |