probably worth remembering with modern cars is that they prioritise lowest part throttle _emissions_ over part throttle economy. TO this end the a/f ratios and timing they have at cruise could actually be improved apon, so relatively speaking, older engines (if well enough developed and sorted by the manufacturer) do a little better at part throttle than their newer rivals.

Mind you, modern engines are getting better and better, all I'm saying is that if they didn't have to meet part throttle NOx emissions targets (for example) they could run leaner a/f ratios and more part throttle timing and use less fuel than they currently do, for the most part (mind you, direct injection and other parameters are closing that gap)