I don't feel that this question has ever been answered satisfactorily, but I don't mean to be inflammatory in any way - I'm just making the general point that brightness is not the same as detail, Indeed, it's not actually even related, properly speaking, but brighter does always sound at least superficially more detailed. And BTW I know what a more resolving hp than the HD 650 sounds like. I have the HD 800!
But to answer the highlighted part of your post, the original reason for asking these questions earlier in the thread was because of this:-
'Very good treble response should give the impression of smooth detail. So many people mistake a bright, sizzly response for good detail. It just ain't so.
'While the HD 660 S was a bit brighter than the other two, it also lacked the nuanced resolution and dynamic balance of the 600/650. Low level details were lost.....'
I don't need/want a rehash of all this (PLEASE), I'm just answering your question.