This setup would definitely play all of those at that resolution. You could get away without doing crossfire, but the combo deal for the graphics card is a great deal and makes it hard to suggest a cheap single card. Id say go with it, everything else looks good.
You can build a q9550 quad core system for about $350 processor, mobo, ram. Throw in a Geforce 260gtx and 500+ watt psu and your sitting about $550-$600 after some rebates. You can pick up a 1080p monitor for under 200 these days, and your all set. That's just what I would do...
"Regardless of the huge variations in the results a fast dual-core or a small triple-core is enough to play the game smoothly. Since the streaming works much better with three or four cores we nevertheless recommend a multi-core processor if you intend to buy a new CPU for Dragon Age: Origins."
As you can see, a 720 gets a smooth 50fps, there isnt any reason wasting money for more fps that your eye can't even notice. (the human eye can't notice any increase in fps after 30fps.) But if you must spend all your cash, get 955 instead.
The gpu here is made to play modern games at max settings at 1900 res, so at it will be overkill at your current resolution.