I would get neither the fx 4300 or the g3258, but instead opt for something like the x4 860k. This is because many aaa titles require a quad core, and the g3258 is of course a dual core. The x4 860k is better value than the 4300, and you get more flexibility in terms of motherboard choice.
http://pcpartpicker.com/list/FBZz6X is my recommendation