You would need to buy a new motherboard for the CPU as well
You should be able to upgrade your mb, cpu, and ps for $300. Then get a cheaper card for around $120 if you shop around (that's what I paid for my 460gtx since I couldn't afford the 560gtx ). but you will definitely be disappointed like I was with the performance boost of just going with a card upgrade as Shinobi-san pointed out.
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