E8400 can reach 4Ghz on air.....
Q6600 can reach around 3.6-4GHZ on air/water
Id personaly get the Q6600, as i render, game, defrag, watch videos and general shizzle alot and more or less at the same time.
Get the Q6600, make sure its the SLACR version, less wattage, less heat, better overclock and also energy efficent!!!
kkthanksbye