I have around 1400mi now and just bought 6qts of motocraft 5w20 syn blend (this is the only motorcraft oil in 5w20 I could find & I would bet it is the factory fill)
I will change it before 1500, then go till 3000mi or so and go to full syn Mobil1 5w20, mobil1 then on every 4000-5000mi
(I've use it since the 80's and never a oil related problem, I have pulled oil pans on 50k & 80k engines that ran mobil1 all or majority of millage and they were clean as new!
IMO don't go to full syn oil till at least 3000 & always change filter at every oil change
I would never sugest any oil change intervil longer then 5000-7500 (even syn) ALL oil will break down over time and crap that gets by the air filter and natural byproducts of a combustion engine get into oil and break it down