For audio, Quad, no contest.
For games (today's games) either or.
For games (tomorrow's games) Quad.
Yes there is a $110 difference but there is also a HUGE difference in overall performance with the right software.
Some might flame you for even comparing these two (even with the price difference), so I warn you.
Anywho, it is worth it all the way my friend.
Unless you save your cash and go with a new Penryn in January. Now THAT is worth it!