sanat1s is a silly answer. Games dont need 6 core processors. Intel doesn't even make 6 core consumer processors. Games ARE becoming more multithreaded but that is really just starting. And either processor should EASILY last 4-5 years. My Phenom II x2 unlocked to a quad and overclocked is still going strong 4 years later.
The 6300 is a good gaming processor for the price. It can be overclocked and its in the sweet spot for gaming. That's why its on the "Best gaming CPU for the money" list and the 8300s are not. Those two extra cores are not going to help for gaming. They DO help with productivity apps but if you aren't going to use it like that then save your money.
As was already said if you do go for an 8300 get the 8320 and bump...