It does represent efficiency, but for most efficiency ain't hugely important is easier to generally build a larger less efficient engine to hit your power and rpm goals.
It not necessarily important in making hp but it's important to where that hp is made rpm wise, In highly competitive race classes with rule restrictions it becomes very important but for most of us if you in the 1.17-1.27+ tq:cid range with a fully built engine your doing ok and your build is above that you can give yourself a nice pat on the back :)
But if you look at the 515 hp @ 5,900 rpm 371 vs 408, the 371 is able to match the 408 peak power and more importantly for this discussion rpm with nothing really exotic, it just seems the top end is science a little better then the 408's. I'm pretty sure it's mainly due velocity and cam specs, the question is what criteria were they using to make these decisions, people on here talk about the importance of velocity but only in some abstract way, and their always concerned about too little but rarely about too much, not about what's is right? And how to figure that out.