Hey, I had old pc with Intel Core Quad 2.5ghz, gts 450 and 4Gb of ram. And I understood that I need to upgrade this old junk. So I bought new motherboard SAM3+ ATX/GA-970A-DS3P GIGA-BYTE and got FX-8320, 8 Gb of ram 1333mhz(Total), and for GPU I got HD 7870 MSI OC 2GB version. For storage I left my old kingston HDD 500GB and 160GB. and all in all it cost for me ~500$+,
my rig is almost the same, except with an 8350 and 16 gigs of ram. plus mines a 7870 sapphire, its ALOT cooler. but you should be able to play any game especially if you tweak it up abit and get the latest drivers :) nice rig though!