Current games will not use the full quad core capabilities.
This is a programming design issue.
Developers are now working on getting games to use the full core capacity so upcoming games will eventually use them well.
The main applications that use the full potential are graphics rendering software like 3D Studio Max or Photpshop.
With what you are doing the only real benefit of getting the quad core is that you can run 4 applications at the same time without affecting the other apps too much as they can use a different core. They will still share the memory though.
The E8500 you has a higher clock speed than the Q6600. If you don't have any applications that support 4 cores, the remaining cores do nothing.
I would suggest the E8500.
