Depends how high up the gaming ladder you want to go.
http://www.hwcompare.com/8999/geforce-gtx-560-ti-vs-geforce-gtx-570/
I doubt either of those cards will run very well with your current psu.
I've had my machine for about 2 years now and I've decided to upgrade it part by part, and i have a couple questions with compatibility.

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