Turbocharged motors are always better off running premium fuel. That said the tune our motor has was designed to run safely off regular unleaded. If Lincoln would have wanted to get more horsepower out of our cars it could have been safely done by changing the tune and making premium a requirement but they didn't they chose to tune the car for unleaded.
So with that said, the car was designed for unleaded and is perfectly safe to run unleaded. I wouldn't of bought the car if it required premium as it would have made the fuel cost on the car outside of the requirement I had set for my wifes new car.
We have been and will continue to run unleaded. So far best we have done was avg of 31mpg on a 200ish mile trip. We have noticed where we get our unleaded does have some impact on the fuel economy but not enough to even consider the added price of premium to be an option.