“Mariah is incorrect. If you use evil omen, then no there is little advantage of having higher than 80 poisoning combined with 120 magery, as you will inflict lethal poison 100% of the time within 3 tiles with poison spell (not even poison field) when using evil omen first at 80 poisoning skill.
Since using necromancy you may enjoy a slightly higher chance of actually poisoning your target (as well as dealing damage) with the necromancy poison strike spell with poisoning at 100 over 80, rare but the higher your poisoning, the higher chance.
You may find a happy medium at 90 poisoning as the poisoning mastery can be advantageous. I couldn’t discern any difference between “tolerance mastery”at 90 over 100 skill. And you may enjoy injected strike as a mage as unlike with weapon specials, believe it or not the toggle does not switch off when casting spells.
If + skill is at a premium to you, consider going for 90 poisoning with 110 magery, over 80/120.”-+-