I lived in Michigan : 9 years (Burton, Kalamazoo)
I used to own 91 Accrod EX sedan.. Auto..
I found out that Mobil 1 5w-30 gets best gas mileage.
(regular Mobil 1 Oil and oil change: Every 3,000 miles)

I also tried Vavoline Semi-Sync. 5w-30 (Summer of 2000)
due to my uncle is Ford fan, Ford uses Vavoline and it was free..
Result: Car runs little bit hotter and gas mileage decreased...

Mixing different types engine oil will not harm your car.
So don't worry. After 3,000 miles change your oil...

PS: Think about the cars that burns oil...