Fuel economy... you also still get better weight distribution because the "missing" 2 cylinders are off the front of the engine so the center of gravity is still quite a bit farther rearward.
I myself like the 3.8L minivan engines, my parents had a 2003 Chrysler Town & Country with the 3.8 and it moved nicely for being almost 2 tons and only having a 4-speed auto trans. Lots of mid-range torque on those engines and they're still pushrod OHV so the heads are nice and skinny. My mom's car is a 2014 Chrysler 300C with the Pentastar and 8-speed and that thing is a rocket up to about 70 MPH (compared to the 5.7 Hemi which she had in an older 300C, that was a beast above 70 MPH) but that would be too much work for me to put one in an A-body. I know the member here who did the Pentastar swap had a lot of trouble with exhaust routing because the Pentastar has the exhaust manifolds cast as part of the head and they exit at bad angles for an A-body installation.
