I think it's funny how ExxonMobil is spinning M1EP as a 15,000 mile oil and M1AP as a 1 year oil. If you look at the specs though, it's:
M1EP 1 year, 15,000 miles, $25 for a 5 quart jug.
M1AP 1 year, 20,000 miles, $50 for a 5 quart jug.
Now, if ExxonMobil would tell us what goes in to their latest and greatest oil, we might get excited. But, they hold the position of "Just look at the specs, don't worry your sweet little head about what's in the oil, that's our job."
Consequently, I think they've painted themselves into a corner. The spec difference doesn't justify the cost difference, and it's against their policy to say just how great their base stocks might be.
Watch for Castrol and Shell to come out with 20k/1 year oils, and then the price will settle down to about $35 for 5 quarts.