Also, the i5 range have K-series CPUs in them (the 2500K and the 3570K) that have their multipliers unlocked for easy overclocking, where as there aren't any CPUs in the i3 range with unlocked multipliers.
Title really need to change from "The fastest processor in the world 2012" to something else. I jumped in to put the answer "the human brain". But the question is totally irrelevant which would make my answer totally wrong.
Also, i3 and i5 different by i3 not having turboboost.