U just opened up a huge can of worms for the amd and intel fan boys, hopefully i can jump in before this thread gets crazy (i really hope it doesnt).
The answer to your question is not really an easy one. Their are games on the market such as BF4 that have been designed to use 8 cores, however their is a huge amount of diminishing returns per core added and not all cores are the same. At the moment most games effectively utilize two to maybe three cores, with higher core cpus barely adding any fps/core.
Now Im assuming you may have heard that new technologies like Mantle or the upcoming DX12 will utilize more cpu cores to increase fps/efficiency, these technologies do not need more cores to function. All they do is simply split up the workload between the cores much more effectively, resulting in less cpu power being needed to run games.
So although their is alot of fighting I would recommend u get the i5 for a couple reasons. 1) its a way more powerful chip in almost every way 2) amd cores are not as strong as intel cores, partially because amd architecuture is designed so the multiple cores share resources 3) atm a i5 4440 will be able to play all main titles without bottlenecking any gpu on the market, the same cannot be said for the fx 8320 4) the i5 is more futureproof
Hope this helps to clarify, also I am not an intel fan boy, but i will say atm they are essentially outperforming amd anywhere past their i3 line of processors.