IF the system has an adequate power supply, I would overclock that i5 to 3,5ghz (optional, but would help alot to rid of bottlenecks) and put in something between HD7750 - HD7870 depending on budget.
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Intel I7 3770K @ 4.5ghz, Cooler Master Hyper 212 Evo, Gigabyte Z77X-UD3H, Gigabyte HD7970 ghz edition, 4x4gb Kingston HyperX Beast 2133mhz, Seasonic Platinum 860, OCZ Vertex 4 128gb, WD Black 1TB, WD Green 3TB+1.5TB, ASUS Xonar Essence ST, ASUS VE278Q, Windows 3.11