Nononono, Quadfire is atrocious, especially when combined with a Phenom II X4.
If you do see it lagging slightly, best course of action would be a HD5870 for Tri-fire.
why is quad fire atrocious? I dont follow/care too much about ati's scaling, mainly as im on an SLI board so till I replace a lot of stuff im not going to need to know.