I've heard bad things about CyberPowerPC. I would definitely suggest building the desktop yourself if you feel like you can do it. Not to mention building yourself will be cheaper, allowing for better components.
Down to brass tax. Given that you'll be doing mostly gaming on your soon-to-be new desktop go with the i5 4670. Better yet you might look into a 4670K (if you're into overclocking). It could give you a good performance boost down the line. Although, and don't quote me on this, Broadwell or at least a Haswell refresh should be coming down the pipe in the next nine months. You might wait it out and see what comes up.