Viscosity really doesn't matter, it's how well the oil is formulated. If you can get teh same wear with a lower viscosity, then use a lower viscosity. It's that simple. Too many people worry about what viscosity to run. Realize that most peole throughout the last 20 years have been running 5w-20 oils and still getting long life out of their cars! Reason being is that most 5w-30's from awhile back sheared down to 5w-20's. Asia is now jumping on board and calling for 20wts as well. I put German Castrol in my Honda and it felt VERY sluggish.
I think the mistake people make is they say, oh it's CAFE, therefore it sucks. Wrong....to compensate for lower viscosity they have improved the anti wear additives. Havoline conventional oils all contain 490ppm of Moly. It's a great oil. Motorcraft said their testing of the 5w-20 outperformed their 5w-30. Go figure.