Well i use a GTX 580 with 4GB 2133MZ RAM and a 2600k @ 4.8 and i can run this game perfect(ish) at MAX settings at a res of 1920x1080.
If you can pick up a second hand 580/570 off eBay, this will be much better performance than a new 660ti for around the same price.
Also, depending on your motherboard and if it can support a quad core CPU, try looking for a used CPU on eBay.
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