Use 10W 30 Mobil 1, but use close to 5 quarts due to using M1-301 , Mustang 5.0-Type Oversized Oil Filter. Big filter seems like a good move.
Dunno, but tests have been done (forget company) on BMW(s) using synthetic, where a car has been run at 150mph (120mph?) for a million miles on a dyno; synthetic oil did not show any breakdown after. And syntheitc was originally used in race cars and used to cost a fortune.
Naturally, with synthetics, the issue on the road is going to be dirt and contaminates, if not breakdown and sludge creation. But, even so, High-end roadcars that come from the factory with Mobil 1 are not listed to receive oil changes but every 15,000 miles. With my Jeep, off-road and such, I err on the side of about 10,000 mile oil changes with synthetic.
And, I did the Bilstein Oil Flush about 2000 miles ago and oil still looks golden. If its still golden at 10,000 I won't change the oil; if not, then I will.