Update: The first 5000 miles of 10w-30 is now complete. I drained it and refilled with a mix of 3qt. of QS 10w-30 and 1.5 qt of M1 0w-20 at exactly 50,000 miles. This will be the "winter" oil change. l use "winter" loosely, since it rarely gets below 40 where I live. When and if it does occur, its only for a day or two. or maybe just overnight.
The 10w-30 performed excellently as far as I could tell. My MPG's are virtually identical to when I ran dealership 5w-20. I am averaging 38.0 mpg mixed. This "winter" mix I installed will last until the spring, when I will resume using straight 10w-30. I am highly. highly confident 10w-30 is perfectly safe to use, at least in warmer areas. Of course I would not suggest it in a Minnesota winter.
This 50,000 miles also marks 5 years of ownership, almost to the day. The Fiesta has been an EXCELLENT vehicle. Zero mechanical issues. One small trim issue where the trim around the windshield lost a piece on the drivers side. I am going to keep this Fiesta for how ever long it runs.