the efficiency depends on the life and armor of the mob, basically how fast you can kill it. if you can kill it before the snd is up then go for it, but soloing i like to just slam the damage home most of the time. i haven't been combat swords in a long time, but for casters slam the damage and if it's high armor then mabye use snd. i dont' like rupture on mobs, only bosses for the most part and pvp. rupture is just a poor alternative to evisc. for a rogue, it hardly ever ticks the whole way through, you'll never get a full rupture. just evisc at the end.