If you're purely after gaming, I suggest you throw most of your budget on your GPU + PSU upgrade. The CPU upgrade will help, but not as much as a good GPU. For now, I think the best-performing compact GPU is this:http://www.amazon.com/MSI-N760-2GD5-OC-ITX/dp/B00HPS4B00/ref=sr_1_1?ie=UTF8&qid=1393131544&sr=8-1&keywords=gtx+760+mini
With a GTX 750 Ti, you won't be able to max out current games (BF4, Crysis 3, Metro: LL, etc) at 1080p. You may be able to get off with High settings though. But I think you would be able to max out the games you mentioned, as they're not that intensive. With the GTX 760 though, you can do a lot, lot more.