Hmm... I rarely, if ever, use Bliz II. Not because of damage, but because of utility. As you get higher up, spells like Fire II are better for damage and can be cast at range. Bliz II puts you in harms way. Only advantage is that with the ice buff up, you can spam Bliz II indefinitely. Then again, I think any THM/BLM worth their salt should be able to manage their MP.