Thinner oil has has better viscosity values, but deminishes the cooling, which in simpler terms breaks the oil down quicker if you just so happen to be born with a heavy right foot like all the rest of us in these forums were. More load = more heat. Going Full synthetic can only do but so much. Yeah, it's true that full synthetic has far better viscosity values than the good ol petroleum based oils do. But you would want to make it slightly thicker to help transfer some of the heat. I thought Most Fords run 5w20 nowadays, so a better upgrade for the summer would be 10w30, or even 10w40 if you're boosted, or boosting. Some engines just aren't designed to run significantly thicker oils. It puts too much wear and tear on the oil pumps because of smaller passages the oil has to go through, the pump has to work that much harder to do the same job. And since you want the best in your engine, it has been proven in most test that royal purple is the best. I think Amsoil or mobil 1 was next in line. I would personally stick with royal purple. It's proven to do the job right.

Damn, I sound like a commercial, lol