hang-the-9 :
First, aside from just wanting to upgrade, why are you upgrading, what issues are you having and in what games?
At the resolution you are using the system at, your system is OK for most things. I'd say your CPU is the worst part of the system for the resolution you are using.
CPU and video care are pretty closely matched, but I would swap out the CPU first (which would mean a full new setup as in the post above) or just leave things as it till you actually have a full reason to buy new parts.
I am wanting to upgrade to get better performance in games such as Just Cause 3, Arma 3, Watch Dogs 2, and other games that are relatively newer. As for the issues go, in some open world games like Just Cause and Watch Dogs, it informs me that I do not have enough memory, and thus I am considering buying like 4GB more of ram to help with that issue. What would be the best available CPU that is compatible with my system? I'd really like to avoid having to get a new mobo and a processor and GPU that are compatible with that just to get better performance because if I were to do that, I'd probably just build a new computer all together.
Edit: Would getting this CPU be worth it for the price or would the performance upgrade not be worth it?
AMD 4 GHz FX-8370 Octa-core Desktop Processor with Wraith Cooler, Black Edition FD8370FRHKHBX