yeah, against boys its like a duracel killing machine but the odds don't favour it with 5++'s and needing 4's to hit.
They only do really do 3-4 wounds a round on average, not enough to kill a nob [usually wounding most of them though] then there's the klaw returns [8 @ ST8 (9 if they charge) and 5 hitting on 3's @ ST10].
**Math-hammer
Dread charges;
5 attacks needing 4's to hit = 2.5 hits
2's to wound with a re-roll [lets consider thats all successfully wounded] = 2.5
5++ save = 1.5 wounds
1.5 further attacks = 0.75 hits
practically auto wounding claws
= 0.75 wounds
5++ save resulting in a less than 50% [0.45] of a further wound.... and that's not being exact. With exact workings [I can't be bothered working it out exactly] it would be slightly less.
I'm not saying that that is what I think will happen, it's what I've found after playing blood angles on a weekly basis... the only unit in my entire army that I am happy to receive a charge from one of those is my Nobz!