Actually, if you have higher intelligence than the mob you're fighting I believe that you have a chance to "amp" or do 1.5x the listed damage. But the amount will be pretty consistent for each mob, it just may vary from mob to mob. For example, with my earth at level 55+ I might to 800 - 1.1k damage to one monster, but then on the next I may only do 500 - 800 because the second mob has higher intelligence than the first.
But basically it still amounts to the same thing - that you should just always pump intelligence and only intelligence (except maybe 5 or 10 into vitality in the beginning) because that's by far the most useful stat to you

Hope that helps. Happy slashing!