Just had had a long talk with my dealers Service Representive and the Regional Warranty Representitive (The guy that decides what gets paid) at my local Ford Dealer about effect of different oil and OCI on warranty.
1. Official Response - Ford recommends 5W20 in your car. Ford recommends 5000 ML changes for most owners.
2. Unofficial Response - Unless you have a obvious oil related failure ie oil is a 5 Weight @ 100C or 70 Weight @ 0C which led directly to a component failure we will not void warranty because of oil.
Basically they have no problem with anything from 0W20 - 20W60 as long as ambient temperatures are within reason. As long as the car does not have obvious signs of maintenance neglect (Major Sludge and/or Acid Damage) they will not ask for proof of OCI or UOA.
Of course since my dealer is also a Saleen Dealer they may be a bit more knowledgeable than most.
Gene