For this game I don't think the x64 runtime provides any additional benefits other than the means to utilize more system memory should it be needed. (Usually this is the case with all titles offering x86 and x64 executables although there might be minor performance gains on 64-bit as well.)
Should the developers choose to they could of course include additional effects to better take advantage of 64-bit capabilities though this isn't very common, Call of Duty: Ghosts is using the additional memory for various things (Though it's 64-bit only.) and Battlefield 4 has cloth physics and some enhanced effects when you start the 64-bit exe.
But again I don't think there's anything special for this game.
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