A GTX 560 shouldn't be bottlenecked by an i5. You'll be okay with your current CPU.
Make sure you upgrade your power supply while you're at it. The Dell one is certain to be garbage, and it'll probably explode if you try running a 560 Ti off of it. I'd recommend a quality 500w or higher. Good brands are Antec, seasonic, cooler master, PC power & cooling, OCZ, and corsair. Don't go with any other brand.
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