I don't know if your agreeing with me since both engines (426 & 5.0) that you say are better than the other bigger engines that you listed but yes efficiency plays a huge role in making HP but larger engines aren't necessarily more efficient at converting fuel and air into HP than smaller ones. If anything the opposite would be true smaller displacement engines tend to be physically smaller so less surface area every where bearing and ring friction more complete combustion than larger bores.
