I think I would suggest, instead, being a Transmuter, and spamming stuff like Haste and Slow. Caster-types can be rocked by a well-placed Flesh to Stone, and opening up giant pits at your enemies' feet with Disintegrate is an amusing prospect.
Well, I've already played him through level 4, so he's stuck as a Conjuration specialist. I certainly plan to CAST haste a lot, and Flesh to Stone is among the ones I've got my eye on later on. Along that route, I was actually considering going all the way to Greater Spell Focus in both Conjuration AND Transmutation, and combine it with something like Persistent Spell and/or Heighten Spell to have a high DC on the caster-type killers, and good DCs on the more area-control effects of the Conjuration school.
And as far as opening pits, I think I'd prefer the Create Pit line instead. I have a feeling (because it'd be what I would do) that creating a pit beneath your enemies with disintegrate would allow some sort of save to not fall in, similar to the Create Pit line. Plus, the Create Pit line starts at level 2 spells.
Honestly, had I seen the Annihilation Lenses, or whatever, I probably would have gone Transmuter first, but them's the breaks.
Is it worth the ridiculous feat investment to get up to Greater Spell Focus in two schools? I mean, are there enough other things worth spending feats on, or will I even need it if I reserve stuff like Flesh to Stone for caster-lookin' enemies?