A few things I have considered to speed things up:
- Each mage starts the game with whatever equipment they wish up to a certain mana cost pre-game.
- Each mage has one side of the arena in which to deploy whatever zone-exclusive conjurations they wish up to a certain mana cost pre-game.
- "Kill Box" mode, where every zone touching a wall instantly kills a mage if they are in them after a certain period of time. In this case, mages do not die from being pushed/teleported/whatever into the kill zones, but must use their next available standard action to move away from the zone or die.
- Victory can be achieved by victory points, which are scored by achieving certain things such as destroying spawn points, doing a certain amount of damage, killing creatures, etc.
Obviously not perfect, but these could be mixed and matched to speed things up.