Right, I would cancel the order on the 4670's. Also, keep in mind if you have an sli motherboard, you cannot run crossfire on that board. The reverse is true as well, if you have a crossfire board, you can't run sli on it as far as I know. These technologies are essentially the same, but from different companies. That's why we recommend one stronger card such as the 4850. Though if you are going to spend 130 dollars you may consider this card.
http://www.newegg.com/Product/Product.aspx?Item=N82E16814121351
It's close in performance to the 4850, but will give you compatibility for newer dx11 games. But you can get the 4850 cheaper. But as mentioned before, 4870 is a great card as well. Either way, any of the options here should make you a very happy camper. Honestly I recommend a single stronger card over sli/crossfire because you avoid more driver and compatibility issues, and don't have to worry whether or not a game supports those features or not. Should be more plug and play in my opinion. Just make sure your power supply can handle whatever card/cards you are putting in.