If you do a lot of multi-tasking like you said, a Q6600 will be perfect for you.
And if you are doing a lot of photoshopping/graphic-wise things on your computer, I'd highly recommend a video card.
photoshop Doesnt Have A 3d Api. It Only Runs On The Processor And Ram... So 4870x2 In Quadruple Sli Will Run At The Same Speed As Integrated Graphics, Unless Of Course Youre Displaying At Some Ridiculously High Resolution...
photoshop Doesn't Require A Good Video Card, I Thought Its More Cpu Dependent, And For Movies, A Cheap 8 Series That Has Purevideo2 (removes Video Stress From The Cpu And Loads It On The Gpu), Like 8400gs Or Something Is Cheap And Would Work With Those Features