if you're gonna tweak mages i'd suggest looking at the way % spell damage increases work, specifically when you stack a few.
with innate legendary bonus, a some spell damage items (+40-50% is quite achievable), legend dark accord, dragon orb mind afire... it gets disgusting pretty quickly.
that said, there may only be a couple of people or even one person able to get the required set to reach the point where it becomes ridiculous... i have personally seen double rends towards the end of dark accord do in excess of 550hp which is pretty gross.
i never bothered to test the arcane power potion from the alchemy quest either, but if it increased the damage further you could probably one round a 600hp tank no problem.