Both are new engines.
My new dream engine puts out 400 HP and gets 40 MPG, if anybody - even BMW makes a turbo 4 banger / trans that does it and the price is right, my 340 is going out and in goes the 4 banger, lol
But back to 2012, a carb engine, maybe a 440 or stroker will cost less and be as powerful and even at 9 mpg it be a longtime for gas savings to pay the extra costs back.
You really believe the new Hemi will get 18 mpg by the way ? I doubt it, if so the 440 would not be getting 9 mpg in the same test, more like 12 - 13 mpg vs `18