I think he already has the e6600 and is wondering if the upgrade to the q6600 is worth it. Not that he wants to choose between the two.
The q6600 is essentially two e6600's. If you can turn around sell the e6600 for a reasonable price, I would say go for it. But if your not running more than one app, or have apps that are seriously multithreaded, I personally dont think it would be worth the money, especially if you cant either sell the e6600 or find another use for it.
If money isn't an issue, than theres no reason to ask, you already chose what you were going to do.