Nowdays you dont look at the processor speed. I would say get dual/quad you can afford, even cheap ones are faster than your old cpu.
Maybe this one: Intel Core i5-760 2.8 GHz
Its quad cpu with loads of power to tagle anything you counter for long time.
And remember, coh is GPU independent
Maybe Nvidia 460 1gb or ATI 6850 (For bigger purse Nvidia 470 / Ati 6870)
For faster loading times its time to upgrade your hardrive to SDD
I suggest OCZ Onyx 2 120 GB 2.5" SSD SATA II
For motherboard i myself prefer Asus boards, take P7p55D Pro
4GB Memory at least.
With this kind of beast you need powersupply that can give you 500W+
Just my thoughts, you asked
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