That depends on which GTX 560 you are considering. At stock speeds, the 6970 is faster (but not faster than the GTX 570, depending on the game). However, most 6970's are sold at stock speeds, while most GTX 560's are sold at factory overclocked speeds. A retail GTX 560 clocked above 900 mhz will beat a 6970 at lower resolutions and match it in overall performance across resolutions.
Of course, there is also about a $120 difference between the cards. The GTX 560's will run much cooler and quieter as well.