I trust i am not showing my ignorance here...it is just that i have never had the opportunity to use poisoned weps in 5th edition.
I just learned while reading through a nid forum that not only do poisoned weps get 4+ or better to wound regardless of toughness...if strength of the user is at least equal to the toughness of the target, the user may reroll all failed wound rolls!
i was about to say that I thought it would be less cool on gaunts than you think, but I caught myself, gaunts are gonna be the premier C'tan killers if that hits the bug 'dex