I would stick with Engineering. Rumour is it's in line for some major loving...
If you're not having too much fun with frost (and I know it's not everyone's cup of tea, but at least you've given it a fair crack of the whip) have you considered a mostly arcane build? It will make your mana pool go a lot further and it would give us the holy trinity for when we hit Karazhan... (ie a frost, fire and arcane mage)