instant death

so with some weapons we have they have instant death on a 6. do they get saves for these? normal saves reanimation? feel no pain? and what about if someone str is 2x our toughness do we get normal saves feel no pain? invul?

Newby here, so please correct me if I am wrong:

You get normal saves, and invulnerable saves in both cases, but no feel no pain.
(2X str leads to instant death which is why the cases are the same I think?)
I have no idea about reanimation protocols

For instant death, be it conferred by a special rule or acquired by doubling the opponent's toughness, you get all applicable armor, cover, or invulnerable saves. Of course you still apply the AP of the weapon you are using. You cannot take feel no pain against ID, and reanimation protocols are reduced by 1. So a 5+ reanimation would be a 6+ against an ID wound.