Quad Core Vs Core i7 - Avid

Guys,
Can someone tell me how much could be the performance difference between a normal Quad Core and Core i7? Cost for basic (CPU + mobo) combo is almost double. Is the difference worth the performance?

if you can afford it, yes it worth it

It doesn't perform poorly in gaming, but it is slightly slower in many games than a similarly clocked C2Q. I've noticed that when I turn off HT, I get better frames especially in Sacred 2.

I wonder if that's because if a game only supports 2 threads, then the second thread goes to a virtual processor and you don't get the same performance as you would if it went to an actual core (like when you turn off HT)? I think it would be cool to see Tom's do a review with HT turned off. Maybe they do already? I should probably look

The sole purpose of this system will be for video editing on Avid.
Can someone, who had some experience on both systems, tell how much time less will i7 take (say for a 15min video file)?
And, will 6GB of RAM be sufficient or adding another 6GB will increase performance to any extent ?

Thanks for the pointer, but unfortunately theres no benchmark for Avid. Every other benchmark says i7 rocks. I guess I will go with i7. But how much ram should i buy? Will Avid really use 12Gig?