For instance if a site traffics 1,000,000,000 page views per day with 50million unique views, does the PPC still matter? What kind of CPM could you expect?
1000M? Are you shure? Why you don't use AdSense? Illegal content or Asian traffic? If your site hasn't any illegal then try to use Fidelity Media and AdBrite. In any case I think you need few networks to be more profitable... Another points highly depend from site quality.