Motorcraft 5W20 is all I have used for 53,000 miles in a V6 Mazda Tribute with 5,000 mile OCIs. My only reference is the timing chain and it's bright and shiny. I'm ~500 miles into an AutoRX cleaning phase now and will let you know what gets loosened up during the rinse. So far the oil is no different than it usually is at 2500 miles. I'll post my results in ~2 months.