As with any rendering programs, you'll need a lot of RAM and video memory. Unless you are working with gigantic rendering projects which require over 2GB of video memory, you should go with a gaming card, because it will be oh so much cheaper. Without knowing what your budget is, though, it's hard to pinpoint what card you'll want. http://www.newegg.com/Product/Product.aspx?Item=N82E16814102914
That will get you where you want to go. Also, get another 4 GB of RAM, making sure it matches what you already have.