Hold your horses.
Since you have a card like the HD 4870 X2, I take it you have a high resolution monitor (Something 1920x1200+). At those high resolutions, the GPU is a lot more stressed that the CPU, therefore the CPU becomes bottlenecked by the GPU. At high resolutions, the Q9550 and an i7 will perform almost identically.
And if you're Q9550's not overclocked, do it!