I wouldn't bother with poisoning, it's no more than a nuisance anymore. Between petals, 4/6 chivalry, healing stone, cure pots, and just plain 'cure poison', most of the time even lethal poison just gets removed. On top of that you have to be almost right next to the guy to apply deadly or lethal.
Scribe is a better bet for the SDI and spell reflect bonus. 15/30 max SDI is only for items, that doesn't count the bonuses you get for stats or skills (inscription, int, eval, or magery). A non-focused Mage with scribe should be almost (-5 %) as good as a focused Mage without.
Of course there's nothing more fun than a Necro Mage that really knows magery inside and out. The curses more than make up for the 15% SDI deficiency. Consider a 6 X 120 Necro Mage (eval, magery, spirit speak, Necro, resist, meditation) if you haven't yet.
I've also seen people drop the resist in that template for petals, apples, and trap boxes, then add spell weaving or inscription. Weaving (pixies, essence of wind, attunement, and the heal over time) is actually not bad, especially when paired with the mana shield mastery.