Uses less power
Not as fast stock speed
No unlocked multi
will not OC as high
average stock speed
will not OC as high as the QX6800
Overall with no price the QX6800 is great. But for the price its not. The Q6700 is good and will OC decently but the Q9550 has a newer process and is about 10% faster clock per clock as well as it will run cooler than the Q6700 at the same clock.
Its not an easy choice. What the hell..... get the Q6000.