dragonsprayer :
the answer depends on the mobo if you have good cooling, water cooling and intel mobo you can crank this beast up!
the 6850 is 65nm and no hafnium
the 9550 is not much better then a q6600 at 3.6ghz, it is but again it depends on the mobo can you get 3.6ghz with your mobo?
its nvidia mobo so high fsb is not its friend! stability issues and high failure rates plague all 80 and 90 services boards
At 9x multiplier (q6600), it's 1600 = 4x400 = 9 x 400 = 3.6ghz. 790i can handle 1600mhz, although higher fsb while remaining stable is unlikely. q9550 use 8.5x multiplier, that's 3.4ghz at 1600mhz fsb, which is fairly good. QX6850 use unlocked multiplier, so fsb is not an issue, and can be oced as high as the cpu will take. The limit is usually 4ghz on air.
Also, if you were comparing a q6600 at 3.6ghz to a q9550 at 2.83ghz, it's not a fair comparison. The oced q6600 will blow away stock q9550 in everything, no exceptions. It's only fair with both cpus oced. On average, 45nm Yorkfield (such as q9550) outperforms 65nm Kentsfield (such as q6600, qx6850) by around 7% per clock. The difference vary greatly depending on task. In games, around 0%, in newer encoding programs that use sse4.1 (which Yorkfield use, but not Kentsfield) the gap can reach 30+%.
For professional encoding, q9550 is the choice, for gaming, either are fine. If you stick to the Nvidia chipset board, qx6850 with unlocked multiplier is the choice, for Intel x38/x48/p45 boards, either are fine.