There will pretty much always be a better CPU or other component to help alleviate the whole future-proof issues, but there are not really many or any games I can list off the top of my head that uses 8 cores. If you want to aim for future proofing I would suggest the 8350 instead of the 8320 or 6300. It offers a higher clock per core and is better for future proofing. There are many games that do not utilize four cores well enough yet, and since noone can predict what requirements there will be in a few years, but four cores will probably be the norm within 3-4 years. And six cores or more, I have no clue when that will become the norm. Also figuring in clock speeds will be increasing for each core, with stock clocks becoming greater to decrease the reason for people to overclock. For example the newer version of one of Intel's CPUs has a .5 GHz increase over the previous similar CPU for stock. So I feel that higher clocks and/or more cores will be fighting it out the next ten years.
So if you are simply playing games, look up the recommended system specs and take a gut instinct. I had a larger budget when I put my PC together so I opted for a lot of cores and other powerful components. But for your budget a graphics card is more important to pair with a good clocked quad core processor, 8 GB RAM, maybe a small SSD for OS only with a normal HDD for everything else. Just my two cents.