my view on engine thermal efficiency

[omgwtfbyobbq]

Yes, large improvements like that on cars are relatively easy following the same pattern, or even just changing gearing. I'd guess that the optimum is ~100mpg@50mph for the average car, or ~50mpg@50mph for the average pickup. Of course, this isn't exactly practical for most in terms of top gear acceleration, so a range of ~50-70mpg and ~30-45mpg is probably a decent combo of practicality and efficiency, w/o going all Basjoos on the vehicle.