Sick haste boost for mages and get really large

So I was questing this morning on my mage, and got the quest [Kill the Cultists] in dragonblight.
On this quest you shall kill a mob named "Anub'ar Cultist" and loot stuff from the mobs.

However, this mob has a spellstealable buff named "Zeal" (Zeal - Spell - World of Warcraft)
that increases you casting speed with 20% and increases your size.
The thing is that this buff stack infinitly so you can get really big and get a lot of haste! I throw almost instant frostfire bolts

Hope this helps a bit!

PS. The mobs are in this area: