I definetly say PSD. Unless this will be a grocery getter making short trips around town. If so, go V10 and accept the 9-11 MPG.
If this will be used for road trips and towing, maybe wait 30 days or so for the new 6.0 ltr PSD with the new 5 spd auto. More $$ but sweet!
Oh, and since the Excursion has such lousy resale (I still want one) I think the PSD will help it hold more value.