Time to upgrade QX6700?

To be frank, no. You spent 1000 on that chip because it could last a long time, and it will. Theres very little games that would benefit from a performance increase in that upgrade, and the QX6700 should last until early next year. Wait for i7.

If you overclock the QX9650 to 3.67, you will see a 15% (or so) increase in CPU speed over the QX6700 at 3.2. This may result in about a 5% increase in overall performance. Is that worth $1K to you?

Save your $$ and be the first kid on the block with a Nehalem rig.