My original post was not to solicit opinion as to the relative merits of various twist rates (though I have no problem with people expressing those opinions) or to get into a p****** contest with others regarding the relative merits of each twist. If you will re-read the original post, you will note that I asked for input from people who had had an aftermarket barrel in 1:7 twist made for their XCR, having already made the decision that for my dollars I wanted a rifle that that was accurate at various distances from close in to long range with any effective bullet weight (55-77 gr) that I might choose.
That said, you may wish to read the extensive, multi part review of the development of the 5.56x45 cartridge by Gil Sengel in Handloader magazine. It was only after the development of the SS109 that the army went to 1:7 twist after first resisting the move. While it is true that the tracer round (being heavier and therefore longer) requires a faster twist, the impetus to change the twist was the SS109 round. If you have references to the contrary I would appreciate your citing them.
Secondly, comparing accuracy of twist rates by the results of different individuals shooting different twists in different rifles at a competition and expecting a valid conclusion is not very objective. If you can cite a true comparison (perhaps from the LE sources you refer to) of the accuracy of various twist rates with different bullet weights at various ranges under controlled circumstances, I would be delighted to read them.
Thirdly, the fact that you are happy with 1:9 twist in your XCR doesn't mean that others don't have different requirements.
Thumbs up - in any weapon deserving of the name, accuracy is only secondary to reliability.