I love to see a nice clean pc. Very Nice ! If you want to overclock your cpu, I would recommend getting an all in one liquid cpu cooler. Only thing I see to upgrade would be your graphics card. How much are you willing to spend? The GTX 780ti is the latest from Nvidia which as of right now is 699.99 U.S. dollars.
The GPU, as Nate said is what needs an upgrade. If you have no price cap, I recommend a Radeon HD7990. If you have a 400ish budget, an R9 280x. If you have a 200ish budget, a GTX760 would be appropriate.
Hows your keyboard & mouse if you're a gamer they make all the difference in the world. I use the corsair m65 its 8200 dpi very fast if you're into shooters you will love it..
Current: MSI Xpower Gaming Titanium | 7700K | G Skill Ripjaws V 3000 16Gb | 960 EVO 500Gb | Intel 730 480Gb | Seasonic 1000 Platinum | NZXT X62 | Acer XB270HU | EVGA 1080 ti FTW3