I'm highly impressed by some of the mileage figures I've seen quoted here for certain GM V6 engines, not just in this thread but over many years. It seems to me that GM is really onto something with these designs and also, I think, is taking a serious engineering interest in efficiency, which I greatly admire. It gives me some additional hope for the company's future. I wish my wife and I could come close to matching these numbers in our VQ30-powered I-30.
I wonder why there doesn't seem to be similar interest in lower-revving, high-efficiency four cylinders. Probably the main issue would be that the press would hate it, and buyers of those cars tend to be highly influenced by such opinions.
BMW tried something like that with the eta engines in the '80's. They weren't push-rod motors, and they were straight sixes, but they were designed to produce good torque at low rpm for high efficiency, and had lower power than their non-eta equivalents. Sure enough the press hated it. BMW forced it on their customers for a few years and consequently sold quite a few, but the idea then died and gas got cheap again. Owners did report excellent mileage, though, and I wonder what something like that could do with today's technology.