According to this guy where he polls the top 100 tactical competition shooters out there... they are pretty evenly split between the 6mm and 6.5 bullet...a smidgin more than half of the top competitors chose the 6mm bullet over the 6.5...but almost all of them are in the 6mm family for that application.
That's what I meant when I said "6mm." I wasn't literally saying a 6mm bullet, but the whole family of .243, .260, .264, 6.5CM, 6.5x47, etc.

Alamo, I know this goes back to another thread/discussion, but I'd really recommend you take a PR/Distance class from one of the nationally recognized schools. Grab a R700 of whatever flavor for cheap and put an optic on there and just go to the class. You'll see a lot of the questions you're asking answered, complete with lab work to prove it (based on what others bring to the class) and it will probably give you a much better foundation rather than relying on internet experts and their mumbo-jumbo.