Meh, i can already hit 4ghz on air with my q6600, i see no point in going to a dual core. This rig is going to stay as is probably until nehalem comes out. If my board fried again though im going to switch to a crossfire setup and flip nvidia the bird.
Also, the way i use my machine, a quad at 3.6 is way better for me than a dual at 4ghz. I always have tons of stuff open, firefox, whatever game i'm playing(with affinity set to all 4 cores), trillian, sometimes listening to streaming music, ventrilo. Ya, my quad gets utilized.