That Core2Quad is still a great processor so you won't have so much problems. I would consider a card between 250$-350$. If you want better framerates, get a GTX670 or a 7950, if you want to save money get a 7870 or a GTX660Ti which i have and works very well. Choose your side, Amd or Nvidia.
This is the model I am using. The graphic card you guys recommend need minimum 500W so do I need to replace the PSU in order for the card to run because, I saw from other thread that some of the user is running on 450W PSU.
I know that the PSU they are using is high quality type, so my question is can my PSU support this card ?