I don't see where NW publishes either a Z or C fare between SEA-FCO. It looks like all they publish is a 9K J fare. You could, however, buy a 3K Z fare to AMS and then a cheapie add-on to Rome. I would probably a Z-fare to AMS, arriving early morning, then a cheap economy ticket departing AMS in the late afternoon/evening. That way you could head into AMS (the airport is only 3.6 euros and 15 minutes away from downtown Amsterdam) for 10 hours or so.