Brammo Motorsports at one time imported a british V8, with a displacement of only 2.0L. I can imagine with a very gentle tune and some TB work, it could be made to get great fuel economy down low.
And you'd have the advantage of 400hp at the same time.
Also, on the topic of your rant, from Ohio to Maine and back, at 65mph on cruise, my mother's 2000 Cadillac Eldorado got 30mpg as recorded by receipts, with a 4.6L V8. In a nearly 5,000lb car. So I know how you feel about the car companies today.