^Good points. If you're interested in those games, or plan to sell them, that's like getting the card for a whole lot less. The HD7870 XT is the stronger card too.
The 660 uses less power though, something to keep in mind depending on the size of your PSU. Even a good 400W PSU will run it, whereas you'll need at least 450W (500W would be better) for the HT7870 XT.