you need to test the game with newer Intel quad cores before saying anything, the game does benefit from more than 4T, but it looks like a fast 4T CPU (like Haswell i5) is great for it, so "need" is not exactly what I would say.
remember the 6 core CPUs have other advantages, cache, memory, clock (for the 3970x), PCIE 3.0 (for AMD cards at least), all of this could contribute to the difference,
if you compare the 2600K with the 3930K the difference is not that big, and the clock difference while running the game I don't know, both have the same turbo for 1c load, but during the game it's probably 200 or 300mhz advantage for the 2600?
but again, 12MB vs 8MB of l3, quad channel memory