I’ve heard that a lower nocking point is better, and it makes sense to me that the more the power stroke of the bow is directly behind the arrow, the more efficient the bow is going to be (assuming good arrow flight, of course). Imagine a nock point way up the string: the arrow would be at an angle to the power stroke. The force vector would be pointed one direction and the arrow pointed in another.
That said, is there any difference between a 5/8” nocking point and a 3/4” nocking point? I doubt it.