Actually, my experience with FG fries is they are larger in size, and I have driven 20 miles with them and even nuking they were better than MDs 5 minutes away.
True, but it takes that larger mass more time to cool, and they still taste like crap when they get cold. That, and the bag is pretty much filled with fries on top of the burgers, so there's much more heat and mass to have to cool over that 20 minutes than McD's at 5.