If these figures were genuine then both engines would need to be fitted with the same size prop (roughly, an APC 10x6 would be close) to get those revs. With that prop then the model would fly much the same with either engine. But load the engine down with bigger props for real world flying (say, somewhere around 11-12,000 revs) and you'd find the smaller engine would be bogging down way below the larger one. The 65 would easily handle a 12x6 or larger but not the 46. The extra low down grunt more than outweighs the extra weight of the larger engine. That extra 6 ounces on a 7.5 pound model is only another 5% extra all up weight.