What do you mean by Melee Spell Caster? Do you mean Arcane Knight using the skill Arcane Blade or Vampiric Blade?
There's no real benefit to pushing to get to Icemist too soon as you still need to build up your character's skill and trait base. So really anytime in the mid-game should do well. Level 10 to Level 18. It's a bit of a wide range as there's a lot of game out there.