Well, the stock Noble in the MM has 2d8 HD, with 9 HP, and a Con of 11. But the Knight's got 8d8+16 HD, with 52 HP and a Con of 14. Archmage has 18d8+18 HD, with 99 HP, and a Con of 12. There's your scale of regular folks you might want to poison.
Now, the three top end poisons are Midnight...