The E6750 should be faster at a single task or doing two seperate ones than the Q6600 as each core is faster.
The only advantage the Q6600 would have would be if something comes out in the future than can utilise all 4 cores at once or if you run more than 2 CPU intensive apps at the same time.
As I said above, the only really CPU intensive stuff I do is music editing, but obviously I don't try to do it at the same time as a full virus scan, so I think the E6750 will be fine, San. I also got the free delivery via AVF, so thanks for that tip off.
I'm not about much tomorrow, so asked for delivery on Thursday, but the case was from Ebuyer, so that may not arrive till Friday. Not much more I can do till then, except to start backing up everything I need off the old machine.