I'm sorry, but rwayne you're absolutely wrong.
The games you want to play, digthis2, are very CPU bound and I too usually have CPU bottlenecking on these same games. Overclocking has helped, sometimes as much as 10 fps, iirc, but my frame rate dips anywhere from 30 - 60, though on average I stay nearer to the 60 end on all of these games. However, I know for a fact that an i5-4670k will make a MASSIVE difference. While I can't say the same for Assassin's Creed IV or Metro Last Light which are both GPU intensive in addition to being somewhat CPU bound, Skyrim and Borderlands 2 are very easy on the GPU and intense as hell on the CPU and they scale ridiculously well with a good CPU.
My friend and I both play Borderlands 2 quite often, and my frame rate stays between 40 - 60 with drops to 30 - 40 somewhat infrequently depending on where I am and what's going on. I have an FX-6300 OC'ed well past your FX-8320 (I'm at 4.5 GHz) and I have a very powerful GTX 770. Conversely, my friend has an i5-3570k and a GTX 660 Ti, a CPU far more powerful than mine and a GPU far weaker than mine, yet his frame rate never dips below 60 (I've played it for hours on his rig as well). I believe he overclocked, but I don't think he got past 4.0 GHz. Still, that should tell you a huge amount about how much the CPU matters in a game.
If you can return the FX-8320 and MOBO and get an i5-4670k and new MOBO for a reduced price, I highly recommend you do so.