You should go read the Dark Eldar codex, as it says somethin along the lines of... Any weapon, can not even wound a Grotesques unless its str is double there toughness in order to inst-kill them... or something very close to this at least. The DE codex is very precise to rule out things such as Sniper fire, Gauss, Witchblades, etc... and actually uses the wording for the minimum Strength required.
And you better believe I asked the guy to prove it to me; then I unloaded a round of fire into those Grotesques from 2 units of 5 Destroyers, and the issue was resolved as I wiped them off the battle field.
Sick isn't it.
PS... I know the Necron Codex quite well thank you, do you know all the other codex' ?
CaHG.