According to wikipedia, the ATI Radeon HD 7xxx series offers twice the performance as the previous generation of graphics cards. Twice the pixel and texture fillrate means twice the overall performance!
http://en.wikipedia.org/wiki/Comparison_of_AMD_graphics_processing_units#Southern_Islands_.28HD_7xxx.29_series
http://en.wikipedia.org/wiki/Comparison_of_AMD_graphics_processing_units#Southern_Islands_.28HD_7xxx.29_series