The FX-8320 is the best rendering value chip on the market. I don't think you will notice much of a performance difference between the FX-8320 and a comparable i5 while playing the game but on the other hand Intel's stronger single threaded performance is advantageous since I don't think the game uses more than two cores anyway. So one chip might be faster while rendering and gaming while the other will certainly be faster during playing the game without rendering.
It is the better rendering/multitasking value chip. Although the game shouldn't be demanding, I don't know if adding a lot of MODs will degrade the performance on the FX chip. If you add recording and running multiple tasks into the equation the FX-8320 may actually perform better. But if you are just playing the game and then the i5 will certainly be the winner.