The naturally aspirated 3.8's knock down 30mpg highway, and Pennsy has plenty of highways.
It's also very hilly, and you want torque to carry you up those hills. 3.8's have plenty of torque.
And, for your information, the Bonnie isn't that big of a car. I've driven big cars. Big cars are friggin Crown Vics and Caprices. A Bonnie is somewhere between an A4 and an A6 in size. Very midsize.
Though it has a bigger back seat than the A6, bigger trunk too. Makes very good use of its FF layout.
And, quite frankly, the earlier Bonnies are pretty handsome for a Camry/Accord competitor.