If you power through quests like that you will quickly run out of quests to do and then you are stuck grinding.

The best way I have found to power level a character is with a healer as backup because heals don't reduce XP gain. In the case of a mage, AoEing helps a lot. Gather up a bunch of creatures and have the priest just spam flash heal on the mage while he AEs them. Also, you can follow a traditional leveling guide (Joana's Guide for example) and just keep the priest on follow constantly topping off your mage. With a strategy like this you can go with a non-traditional spec that maximizes damage done instead of survivability.

Unfortunately, outside of AoE grinding powerleveling a mage is one of the harder classes because they are limited by mana instead of health, like most classes (warrior, hunter, paladin, rogue, warlock are all *really* easy to power level with a priest/paladin/shaman/druid backup because you can spec pure damage and skip all damage reduction talents/gear).