Everyone will have different opnions on this.
I change my engine oil with Royal Purple 10W30 and
a Motorcraft oil filter every three months or three thousand miles.
That is only four oil changes a year wow.
Its actually not recommended to run synthetic oil at all in a vehicle with forced induction, but do what you will.
As for my N/A Explorer.....I run it for twice as long as I did with the previous conventional oil. Changing it about every 12,000-14,000km and changing the filter about every 6,000-7,000km.
I dont know about you guys, but I dont go by the whole extended interval stuff... By the time 3k rolls around, my oil isnt exactly what I would call clean anymore. I use Motorcraft also, but I still change it at 3k just cause its not that clean.
Your only saving a few bucks and a few mins of your time by going a few extra thousand miles.
well i change it every 6-7K miles even if its dark it dont bother me, since i know that german cars have a 10-15K service interval with synthetic oil and that oil comes out dark i know since i use to work for mercedes