I am in the process of doing just the same thing. I was agonizing over spending $$$ to upgrade to either the LGA1366/X58 or waiting a few weeks for the Sandy Bridge to come out and upgrading then. In the end I think what I really want is the LGA2011 so I can put in more ram with larger bandwidth (I do mostly photo/video editing). This means I will have to wait another 9 months or so for the LGA2011 (Q3/2011?) to come out. Ultimately I decided to upgrade my Q6600 system for the short term. For me one of the biggest improvements was buying a solid state drive. The system boots really quick now and the programs seem much speedier. Might also be the fresh install of Win7.
Loaded 64-bit Win7 Professional and all other programs (mostly Lightroom and Photoshop) on this:
OCZ Vertex 2 OCZSSD3-2VTX90G 3.5" 90GB SATA II MLC
http://www.newegg.com/Product/Product.aspx?Item=N82E16820227601
And I bought a used processor (QX6850) and Nvidia 8800 GTX off ebay for around $200 and $67 respectively. I would have really liked to go with the QX9650 or QX9770, but those are both much more expensive than the $200 I spent on the QX6850. Hopefully these will boost the system a bit more.
Hope that helps,
Jason