Anecdotally, there have been a few

I read the book a while ago, but something tells me that book, "Not a Good Day to Die" by Sean Naylor might touch on it.  It's about Operation Anaconda in Afghanistan.  I don't recall any details about twisting elevation knobs, but I think I recall him citing some of them had A2's and the contact distances were not up close and personal.  Meaning far off.  

But I don't know if I'm remembering it correctly about the A2's.  I know he kept saying the Army SF or Green Beret's (or Ranger's) were always grabbing their "M4's and M9's".  But I believe the 10th Mountain was there supporting with mortars and other patrols and some of them might have had A2's.  I might be not remembering that right though.  I'd have to read it again.  But if you feel like picking it up, I thought it was worth reading.

Check the National Match service rifle board.  

Those guys are getting 600yd elevation, probably more if you bottom your front sight, maybe file it some.
Of course seems like 600yds is pretty reasonable distance using 77gr bthp ammo which is basically the
longest and heaviest that will feed when magazine length seated.

Seem to recall the settings being 2 clicks up from bottom for 200yds then max or near max for 600.

any of them in Iraq or Afghanistan were probably Marines. For a really long time the Army had this idea that 300m was the farthest the M16A2 would shoot -- I never had any PMI go over the elevation drum or its use in the Army until I went to SDM school.

I think some are confused. 600m is for the removable carry handles. The fixed upper A2 has an 800m adjustment and was rated to 800m by the mil, i have the manual. From what i have seen the ratings were always based on the adjustability of the sights, and didnt really have anything to do with the 5.56 round or barrel length.

People who say 5.56 isnt lethal need to realize that a lot of people arent breathing because of .22lr and 5.56 at 1000 yards is still comparable to .22lr at close range. If anything works against the round at distance, its the drop, not the projectile itself or ballistics. In the hands of a capable shooter, i would expect the rifle to be deadly far far past 300m, as long as its put on target.

I remeber reading a sniper story about Iraq where they said they would lay their rounds out in the sun to cook them and get as much velocity out of em as possible. But they were talking, 5.56, 7.62 and .300 win mag. And i have no idea how to find that again it was some time back....

Never shot the A2 competitively while on active duty but remember the 500 yard line was my favorite.

The Army set up for A2 rear sights was the sight bottomed out 8/3 and using the large apature for engagements less than 200yds.

The Marine Corps retimed the rear sight to go 2 clicks down from 8/3 and use the small apature for all engagements with the exception of low light/night shooting due to the sharper sight picture.