I have to disagree Tom. The Zetec has a history of sticking valves when filled with heavy weight oil. You most likely do not have this problem as you generate a significantly greater amount of heat than the average Focus, and, therefore, thin the oil much faster than most. While there may have been some changes to the motor that have eliminated this problem (like the elimination of hydraulic lifters), why take the chance?
While I will not be one to say 5w-20 or nothing, I will state that there is no reason to run such a thick oil for a daily driver. What possible benfit could there be?