this is probably due to Nvidia pushing up the default clocks speeds of their 660 to beat AMD's 7800's at stock clocks. It's what they did with their 680's to claim the "performance crown" (at stock). Which would explain why at retail there's very few 680's and 660's not coming out until much later. I really would like to see some benchmarks with both cards running the same memory and GPU core clocks.