skulltaker is just plain dumb... he rends alot more as he doesn't need just a 6, plus any rending wounds he causes inflict 'Instant Death!'...
character killer plain and simple! mind, the tyranids & the daemon prince from the chaos marine codex won't care, beyond the annoying high rending rate skulltaker gets.
still, i actually prefer the fantasy daemon book... i think overall the daemons are ALOT! nastier in fantasy - especially with characters like kairos fateweaver who's arguably the most potent magiker in the entire game! (hint: he can take 14 spells!!!
)
cheers!