Single Player isn't as stressful as playing 64 player maps.
Any new i5 will have no issues in gaming. If you want to have fun and play with overclocking then get the fx, otherwise the i5 is excellent at stock. A overclocked fx will game like a i5. I have yet to see consistent reviews showing the fx-83xx is better. So, go with i5 for ease but get fx if you like overclocking for fun.