Since price is of little concern, you may want to consider other factors.
Ford marketing info says the efficiency of their filters are "targeted removal of 80% or more of particles larger than 20 microns from your oil."
Mobil, on the other hand says, "99.2 percent efficiency rating (under SAE J1858 Multi-Pass Efficiency Test." Advantage Mobil, IMO.
The 820S ADBV is the thread-end style. Mobil has the dome-end style. If the filter on your 4.6 installs on an angle, I'd say the advantage rests with Motorcraft on this feature, IMO.
If you are running extended OCI's, I'd say the Mobil 1 filter is a better choice for efficiency and capacity reasons, IMO.
Either way, you cna't go wrong. Both filters are two of the better choices available these days, again...IMHO.
BTW, if your Mobil filter is only $2 more than the Mobil, you may want to shop around for better prices. Most 820S Motorcraft filters retail around here for $3-4 while the Mobil 1 filters go for $10. Uhm, or let me know where you are getting that bargain on Mobil filters!!!