Forget CAFE and all other debates about regular 5W-30 vs 5W-20. This question relates only to the EP formulation.
If one is looking to extend the drain to 15,000 miles or more, does the 5W-30 outperform the 5W-20 as it gets further into the interval? Suppose by 13,000 miles, fuel dilution starts to factor heavily, wouldn't that reduce the viscosity of the 5W-20 to a more dangerous, protection level than the 5w-30?