I want to but a graphic card but I am having hard time chosing one. Should I be more concerned by bit rate whether 128 bit or 256 bit, or should I be more concerned about the engine clock and memory clock rates? Asus Extreme N6600GT Silencer/HTD has a high engine clock (500 MHZ) and a high memory clock (1GHz - 500 MHz DDR3) but it has a memory interface of 128-bit. On the other hand I found Asus Extreme N6800LE/HTD has a rather lower engine clock (350 MHZ) and a lower memory clock (600 MHz - 300 MHz DDR) but it has a memory interface of 256-bit. Could you help me with that?