Ford (and I'm sure others) have done some interesting things to allow turbos, high boost, and high output on the modern engines while also getting really good fuel economy and running 87. My understanding is it comes to higher compression than what you'd expect, very retarded ignition timing and very rich mixtures under higher boost levels, and I'm sure some other items thrown in like EGR to help. When driving an Ecoboost Mustang it lets you look at the AFR, and towards the top end it gets down in the 10:1 range. I didn't see timing, but I imagine it's retarded a lot.
@jesse has a 3.5 EcoBoost that he tows his camper with, and with the ap he has to see what the computer is doing I think it's shown as much as 5-10 degrees ATDC for timing (yes, ATDC not BTDC).
The engine's optimized for around town and the EPA tests as far as mileage goes, so it makes sense the 5.0 will get better mileage while towing. Really, it's a pretty smart way to do things and something I've thought about for a long time. The concept is not unlike what we do on higher powered aircraft engines, too.