I battled with stability above 485 fsb with my q6600, i ended up giving up since my current 4 x 1gb setup wont go beyond 1165-1170mhz no matter how finely i adjust the sec/ter timings and fine tune the dram controller / channel voltages. I believe if i could run 1200mhz on these sticks there would be a fighting chance to get close to 500 fsb stable on my board.